Method and apparatus for performing device to device communication in wireless communication system

ABSTRACT

This specification provides a method for performing a discovery procedure in a wireless communication system supporting device to device (D2D) communication. The method is performed by first user equipment and includes monitoring a discovery resource region, selecting a discovery resource for transmitting a discovery message in the discovery resource region, and transmitting the discovery message to second user equipment through the selected discovery resource. The selected discovery resource includes a discovery resource having a received energy level corresponding to a threshold value or less or a threshold value or higher.

This application is a 35 USC § 371 National Stage entry of InternationalApplication No. PCT/KR2014/010382, filed on Oct. 31, 2014, and claimspriority to U.S. Provisional Application Nos. 61/897,832, filed Oct. 31,2013, 61/900,350, filed Nov. 5, 2013, and 61/929,488, filed Jan. 20,2014 all of which are incorporated by reference in their entiretyherein.

TECHNICAL FIELD

This specification relates to device to device (D2D) communication in awireless communication system, and more particularly, to a method andapparatus for performing a discovery procedure for D2D communication.

BACKGROUND ART

Mobile communication systems have been developed to provide voiceservices while ensuring the activity of a user. However, the mobilecommunication systems have been expanded to their regions up to dataservices as well as voice. Today, the shortage of resources is causeddue to an explosive increase of traffic, and more advanced mobilecommunication systems are required due to user's need for higher speedservices.

Requirements for a next-generation mobile communication system basicallyinclude the acceptance of explosive data traffic, a significant increaseof a transfer rate per user, the acceptance of the number ofsignificantly increased connection devices, very low end-to-end latency,and high energy efficiency. To this end, research is carried out onvarious technologies, such as dual connectivity, massive Multiple InputMultiple Output (MIMO), in-band full duplex, Non-Orthogonal MultipleAccess (NOMA), the support of a super wideband, and device networking.

Direction communication between devices, that is, device-to-device (D2D)communication, refers to a communication method for setting up a directlink between a plurality of devices (e.g., a plurality of types of userequipments (UE) and directly exchanging voice and data between theplurality of devices without the intervention of an evolved NodeB (eNB).

D2D communication may include methods, such as UE-to-UE communicationand peer-to-peer communication. Furthermore, the D2D communicationmethod may be applied to machine-to-machine (M2M) communication andmachine type communication (MTC).

D2D communication has been taken into consideration as one of methodscapable of solving the burden of an eNB attributable to data trafficthat is suddenly increased. For example, in accordance with D2Dcommunication, overhead of a network can be reduced because data can beexchanged between devices without the intervention of an eNB unlike inan existing wireless communication system.

Furthermore, if D2D communication is adopted, effects, such as areduction of some of the procedures of an eNB, a reduction of powerconsumed by devices participating in D2D, an increase of a data transferrate, an increase of the accommodation ability of a network, a loaddistribution, and the expansion of cell coverage, can be expected.

DISCLOSURE Technical Problem

An object of this specification is to provide a method for determining(or selecting) a resource in order to send a discovery message indiscovery using D2D communication.

Furthermore, an object of this specification is to provide a method forsolving a resource collision problem, which may occur due to theselection of the same resource between types of UE, by measuring thereceived energy levels of discovery resources in discovery using D2Dcommunication.

Furthermore, an object of this specification is to provide a method forsolving a resource collision problem, which may occur due to theselection of the same resource between types of UE, by clustering (orgrouping) and randomly selecting discovery resources in discovery usingD2D communication.

Technical objects to be achieved in this specification are not limitedto the aforementioned objects, and those skilled in the art to which thepresent invention pertains may evidently understand other technicalobjects from the following description.

Technical Solution

This specification provides a method for performing a discoveryprocedure in a wireless communication system supporting device to device(D2D) communication. The method is performed by first user equipment andincludes monitoring a discovery resource region, selecting a discoveryresource for sending a discovery message in the discovery resourceregion, and sending the discovery message to second user equipmentthrough the selected discovery resource. The selected discovery resourceincludes a discovery resource having a received energy levelcorresponding to a threshold value or less or a threshold value orhigher.

Furthermore, in this specification, the discovery resource regionincludes 64 subframes.

Furthermore, in this specification, the discovery message is transmittedthrough the selected discovery resource in a first discovery period andtransmitted through a discovery resource changed according to apredetermined hopping pattern from a subsequent discovery period.

Furthermore, in this specification, the selected discovery resource israndomly selected from resources having received energy levelscorresponding to a threshold value or less.

Furthermore, in this specification, the selected discovery resourceincludes a unit resource unit.

Furthermore, in this specification, selecting the discovery resourceincludes selecting one of one or more discovery resource groups,selecting one sub-discovery resource group by performing randomselection on sub-discovery resource groups of the selected discoveryresource group, and selecting one unit resource unit by performingrandom selection on unit resource units of the selected sub-discoveryresource group.

Furthermore, in this specification, the discovery resource groupincludes at least two unit resource units, and the discovery resourcegroup includes at least one sub-discovery resource group.

Furthermore, in this specification, the discovery resource group isdetermined using channel status information of reference signal receivedpower (RSRP) or reference signal received quality (RSRQ) or informationabout a position of the user equipment.

Furthermore, in this specification, the method further includesmonitoring the discovery resource region for each discovery resourcegroup, and determining whether or not to send the discovery message in aspecific discovery resource group based on a result of the monitoring.

Furthermore, in this specification, whether or not to send the discoverymessage in the specific discovery resource group is determined by takinginto consideration a ratio of high and low energy levels of unitresource units within the specific discovery resource group.

Furthermore, this specification provides first user equipment performinga discovery procedure in a wireless communication system supportingdevice to device (D2D) communication. The first user equipment includesa communication unit configured to send and receive radio signals to andfrom the outside and a processor functionally coupled to thecommunication unit. The processor performs control so that a discoveryresource region is monitored, a discovery resource for sending adiscovery message is selected in the discovery resource region, and thediscovery message is transmitted to second user equipment through theselected discovery resource. The selected discovery resource includes adiscovery resource having a received energy level corresponding to athreshold value or less or a threshold value or higher.

Furthermore, in this specification, the processor performs control sothat one of one or more discovery resource groups is selected, onesub-discovery resource group is selected by performing random selectionon sub-discovery resource groups of the selected discovery resourcegroup, and one unit resource unit is selected by performing randomselection on unit resource units of the selected sub-discovery resourcegroup.

Furthermore, in this specification, the processor performs control sothat the discovery resource region is monitored for each discoveryresource group and whether or not to send the discovery message in aspecific discovery resource group is determined based on a result of themonitoring.

Furthermore, in this specification, whether or not to send the discoverymessage in the specific discovery resource group is controlled by takinginto consideration a ratio of high and low energy levels of unitresource units within the specific discovery resource group.

Advantageous Effects

This specification has an advantage in that D2D communication can besmoothly performed because the method for determining a resource regionin order to send a discovery message in discovery using D2Dcommunication is provided.

Furthermore, this specification has an advantage in that a collisionbetween resources which may occur due to the selection of the sameresource between types of UE can be prevented because the receivedenergy levels of discovery resources are measured and regions throughwhich types of UE send discovery messages are differently configured.

Furthermore, this specification has an advantage in that a collisionbetween resources which may occur due to the selection of the sameresource between types of UE can be prevented because discoveryresources are clustered (or grouped) and randomly selected and regionsthrough which types of UE send discovery messages are differentlyconfigured

Advantages which may be obtained in this specification are not limitedto the aforementioned advantages, and various other advantages may beevidently understood by those skilled in the art to which the presentinvention pertains from the following description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the present invention and are incorporated into andconstitute a part of this application, illustrate embodiments of thepresent invention and, together with the description, serve to explainthe principle of the invention.

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 5 shows an example of a form in which PUCCH formats are mapped tothe PUCCH regions of an uplink physical resource block in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 6 shows the structure of a CQI channel in the case of a normal CPin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 7 shows the structure of ACK/NACK channels in the case of a normalCP in a wireless communication system to which an embodiment of thepresent invention may be applied.

FIG. 8 shows an example in which 5 SC-FDMA symbols are generated andtransmitted during one slot in a wireless communication system to whichan embodiment of the present invention may be applied.

FIG. 9 shows an example of component carriers and carrier aggregationsin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 10 shows an example of the structure of a subframe according tocross-carrier scheduling in a wireless communication system to which anembodiment of the present invention may be applied.

FIG. 11 shows an example of the transport channel processing of UL-SCHsin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 12 shows an example of the signal processing process of an uplinkshared channel, that is, a transport channel, in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 13 shows the configuration of a known multiple input and multipleoutput antenna (MIMO) communication system.

FIG. 14 is a diagram showing a channel from a plurality of transmissionantennas to one reception antenna.

FIG. 15 illustrates a reference signal pattern mapped to a pair ofdownlink resource blocks in a wireless communication system to which anembodiment of the present invention may be applied.

FIG. 16 illustrates an uplink subframe including a sounding referencesignal symbol in a wireless communication system to which an embodimentof the present invention may be applied.

FIG. 17 illustrates the segmentation of a relay node resource in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 18 is a diagram conceptually illustrating D2D communication in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 19 shows an example of various scenarios for D2D communication towhich methods proposed in this specification may be applied.

FIG. 20 is a diagram showing an example of a discovery procedure betweentypes of UE.

FIG. 21 is a flowchart illustrating an example of a method for selectinga discovery region in a discovery procedure proposed in thisspecification.

FIG. 22 is a diagram showing an example of a method for selecting adiscovery region in a discovery procedure proposed in thisspecification.

FIG. 23 is a diagram showing another example of a method for selecting adiscovery region in a discovery procedure proposed in thisspecification.

FIG. 24 illustrates that a collision between resources is generatedbecause the same hopping pattern that has been previously defined (orpredefined) is selected after a discovery resource is selected.

FIG. 25 is a flowchart illustrating an example of a method forpreventing a resource collision problem which may occur in a discoveryprocedure proposed in this specification.

FIG. 26 is a diagram showing an example of a method for preventing aresource collision problem in a discovery procedure proposed in thisspecification.

FIG. 27 is a diagram showing another example of a method for preventinga collision between resources in a discovery procedure proposed in thisspecification.

FIG. 28 is a diagram showing yet another example of a method forpreventing a collision between resources in a discovery procedureproposed in this specification.

FIG. 29 is a diagram showing an example of the internal block diagramsof UE and an eNB may be implemented in the methods proposed in thisspecification.

MODE FOR INVENTION

Hereafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Adetailed description to be disclosed hereinbelow together with theaccompanying drawing is to describe embodiments of the present inventionand not to describe a unique embodiment for carrying out the presentinvention. The detailed description below includes details in order toprovide a complete understanding. However, those skilled in the art knowthat the present invention can be carried out without the details.

In some cases, in order to prevent a concept of the present inventionfrom being ambiguous, known structures and devices may be omitted or maybe illustrated in a block diagram format based on core function of eachstructure and device.

In the specification, a base station means a terminal node of a networkdirectly performing communication with a terminal. In the presentdocument, specific operations described to be performed by the basestation may be performed by an upper node of the base station in somecases. That is, it is apparent that in the network constituted bymultiple network nodes including the base station, various operationsperformed for communication with the terminal may be performed by thebase station or other network nodes other than the base station. A basestation (BS) may be generally substituted with terms such as a fixedstation, Node B, evolved-NodeB (eNB), a base transceiver system (BTS),an access point (AP), and the like. Further, a ‘terminal’ may be fixedor movable and be substituted with terms such as user equipment (UE), amobile station (MS), a user terminal (UT), a mobile subscriber station(MSS), a subscriber station (SS), an advanced mobile station (AMS), awireless terminal (WT), a Machine-Type Communication (MTC) device, aMachine-to-Machine (M2M) device, a Device-to-Device (D2D) device, andthe like.

Hereinafter, a downlink means communication from the base station to theterminal and an uplink means communication from the terminal to the basestation. In the downlink, a transmitter may be a part of the basestation and a receiver may be a part of the terminal. In the uplink, thetransmitter may be a part of the terminal and the receiver may be a partof the base station.

Specific terms used in the following description are provided to helpappreciating the present invention and the use of the specific terms maybe modified into other forms within the scope without departing from thetechnical spirit of the present invention.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), non-orthogonal multiple access (NOMA), and the like. The CDMAmay be implemented by radio technology universal terrestrial radioaccess (UTRA) or CDMA2000. The TDMA may be implemented by radiotechnology such as Global System for Mobile communications (GSM)/GeneralPacket Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution(EDGE). The OFDMA may be implemented as radio technology such as IEEE802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, E-UTRA (Evolved UTRA),and the like. The UTRA is a part of a universal mobile telecommunicationsystem (UMTS). 3^(rd) generation partnership project (3GPP) long termevolution (LTE) as a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) adopts the OFDMA in a downlink and theSC-FDMA in an uplink. LTE-advanced (A) is an evolution of the 3GPP LTE.

The embodiments of the present invention may be based on standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2 whichare the wireless access systems. That is, steps or parts which are notdescribed to definitely show the technical spirit of the presentinvention among the embodiments of the present invention may be based onthe documents. Further, all terms disclosed in the document may bedescribed by the standard document.

3GPP LTE/LTE-A is primarily described for clear description, buttechnical features of the present invention are not limited thereto.

General System

FIG. 1 illustrates a structure a radio frame in a wireless communicationsystem to which the present invention can be applied.

In 3GPP LTE/LTE-A, radio frame structure type 1 may be applied tofrequency division duplex (FDD) and radio frame structure type 2 may beapplied to time division duplex (TDD) are supported.

FIG. 1(a) exemplifies radio frame structure type 1. The radio frame isconstituted by 10 subframes. One subframe is constituted by 2 slots in atime domain. A time required to transmit one subframe is referred to asa transmissions time interval (TTI). For example, the length of onesubframe may be 1 ms and the length of one slot may be 0.5 ms.

One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in the time domain and includes multipleresource blocks (RBs) in a frequency domain. In 3GPP LTE, since OFDMA isused in downlink, the OFDM symbol is used to express one symbol period.The OFDM symbol may be one SC-FDMA symbol or symbol period. The resourceblock is a resource allocation wise and includes a plurality ofconsecutive subcarriers in one slot.

FIG. 1(b) illustrates frame structure type 2. Radio frame type 2 isconstituted by 2 half frames, each half frame is constituted by 5subframes, a downlink pilot time slot (DwPTS), a guard period (GP), andan uplink pilot time slot (UpPTS), and one subframe among them isconstituted by 2 slots. The DwPTS is used for initial cell discovery,synchronization, or channel estimation in a terminal. The UpPTS is usedfor channel estimation in a base station and to match uplinktransmission synchronization of the terminal. The guard period is aperiod for removing interference which occurs in uplink due tomulti-path delay of a downlink signal between the uplink and thedownlink.

In frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether the uplink and the downlinkare allocated (alternatively, reserved) with respect to all subframes.Table 1 shows the uplink-downlink configuration.

TABLE 1 Downlink- to-Uplink Uplink- Switch- Downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

Referring to Table 1, for each sub frame of the radio frame, ‘D’represents a subframe for downlink transmission, ‘U’ represents asubframe for uplink transmission, and ‘S’ represents a special subframeconstituted by three fields such as the DwPTS, the GP, and the UpPTS.The uplink-downlink configuration may be divided into 7 configurationsand the positions and/or the numbers of the downlink subframe, thespecial subframe, and the uplink subframe may vary for eachconfiguration.

A time when the downlink is switched to the uplink or a time when theuplink is switched to the downlink is referred to as a switching point.Switch-point periodicity means a period in which an aspect of the uplinksubframe and the downlink subframe are switched is similarly repeatedand both 5 ms or 10 ms are supported. When the period of thedownlink-uplink switching point is 5 ms, the special subframe S ispresent for each half-frame and when the period of the downlink-uplinkswitching point is 5 ms, the special subframe S is present only in afirst half-frame.

In all configurations, subframes #0 and #5 and the DwPTS are intervalsonly the downlink transmission. The UpPTS and a subframe justsubsequently to the subframe are continuously intervals for the uplinktransmission.

The uplink-downlink configuration may be known by both the base stationand the terminal as system information. The base station transmits onlyan index of configuration information whenever the uplink-downlinkconfiguration information is changed to announce a change of anuplink-downlink allocation state of the radio frame to the terminal.Further, the configuration information as a kind of downlink controlinformation may be transmitted through a physical downlink controlchannel (PDCCH) similarly to other scheduling information and may becommonly transmitted to all terminals in a cell through a broadcastchannel as broadcasting information.

The structure of the radio frame is just one example and the numbersubcarriers included in the radio frame or the number of slots includedin the subframe and the number of OFDM symbols included in the slot maybe variously changed.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin the wireless communication system to which the present invention canbe applied.

Referring to FIG. 2, one downlink slot includes the plurality of OFDMsymbols in the time domain. Herein, it is exemplarily described that onedownlink slot includes 7 OFDM symbols and one resource block includes 12subcarriers in the frequency domain, but the present invention is notlimited thereto.

Each element on the resource grid is referred to as a resource elementand one resource block includes 12×7 resource elements. The number ofresource blocks included in the downlink slot, N^(DL) is subordinated toa downlink transmission bandwidth.

A structure of the uplink slot may be the same as that of the downlinkslot.

FIG. 3 illustrates a structure of a downlink subframe in the wirelesscommunication system to which the present invention can be applied.

Referring to FIG. 3, a maximum of three fore OFDM symbols in the firstslot of the sub frame is a control region to which control channels areallocated and residual OFDM symbols is a data region to which a physicaldownlink shared channel (PDSCH) is allocated. Examples of the downlinkcontrol channel used in the 3GPP LTE include a Physical Control FormatIndicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH),a Physical Hybrid-ARQ Indicator Channel (PHICH), and the like.

The PFCICH is transmitted in the first OFDM symbol of the subframe andtransports information on the number (that is, the size of the controlregion) of OFDM symbols used for transmitting the control channels inthe subframe. The PHICH which is a response channel to the uplinktransports an Acknowledgement (ACK)/Not-Acknowledgement (NACK) signalfor a hybrid automatic repeat request (HARQ). Control informationtransmitted through a PDCCH is referred to as downlink controlinformation (DCI). The downlink control information includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for apredetermined terminal group.

The PDCCH may transport A resource allocation and transmission format(also referred to as a downlink grant) of a downlink shared channel(DL-SCH), resource allocation information (also referred to as an uplinkgrant) of an uplink shared channel (UL-SCH), paging information in apaging channel (PCH), system information in the DL-SCH, resourceallocation for an upper-layer control message such as a random accessresponse transmitted in the PDSCH, an aggregate of transmission powercontrol commands for individual terminals in the predetermined terminalgroup, a voice over IP (VoIP). A plurality of PDCCHs may be transmittedin the control region and the terminal may monitor the plurality ofPDCCHs. The PDCCH is constituted by one or an aggregate of a pluralityof continuous control channel elements (CCEs). The CCE is a logicalallocation wise used to provide a coding rate depending on a state of aradio channel to the PDCCH. The CCEs correspond to a plurality ofresource element groups. A format of the PDCCH and a bit number ofusable PDCCH are determined according to an association between thenumber of CCEs and the coding rate provided by the CCEs.

The base station determines the PDCCH format according to the DCI to betransmitted and attaches the control information to a cyclic redundancycheck (CRC) to the control information. The CRC is masked with a uniqueidentifier (referred to as a radio network temporary identifier (RNTI))according to an owner or a purpose of the PDCCH. In the case of a PDCCHfor a specific terminal, the unique identifier of the terminal, forexample, a cell-RNTI (C-RNTI) may be masked with the CRC. Alternatively,in the case of a PDCCH for the paging message, a paging indicationidentifier, for example, the CRC may be masked with a paging-RNTI(P-RNTI). In the case of a PDCCH for the system information, in moredetail, a system information block (SIB), the CRC may be masked with asystem information identifier, that is, a system information (SI)-RNTI.The CRC may be masked with a random access (RA)-RNTI in order toindicate the random access response which is a response to transmissionof a random access preamble.

FIG. 4 illustrates a structure of an uplink subframe in the wirelesscommunication system to which the present invention can be applied.

Referring to FIG. 4, the uplink subframe may be divided into the controlregion and the data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) transporting uplink control information isallocated to the control region. A physical uplink shared channel(PUSCH) transporting user data is allocated to the data region. Oneterminal does not simultaneously transmit the PUCCH and the PUSCH inorder to maintain a single carrier characteristic.

A resource block (RB) pair in the subframe are allocated to the PUCCHfor one terminal. RBs included in the RB pair occupy differentsubcarriers in two slots, respectively. The RB pair allocated to thePUCCH frequency-hops in a slot boundary.

Physical Uplink Control Channel (PUCCH)

The uplink control information (UCI) transmitted through the PUCCH mayinclude a scheduling request (SR), HARQ ACK/NACK information, anddownlink channel measurement information.

The HARQ ACK/NACK information may be generated according to a downlinkdata packet on the PDSCH is successfully decoded. In the existingwireless communication system, 1 bit is transmitted as ACK/NACKinformation with respect to downlink single codeword transmission and 2bits are transmitted as the ACK/NACK information with respect todownlink 2-codeword transmission.

The channel measurement information which designates feedbackinformation associated with a multiple input multiple output (MIMO)technique may include a channel quality indicator (CQI), a precodingmatrix index (PMI), and a rank indicator (RI). The channel measurementinformation may also be collectively expressed as the CQI.

20 bits may be used per subframe for transmitting the CQI.

The PUCCH may be modulated by using binary phase shift keying (BPSK) andquadrature phase shift keying (QPSK) techniques. Control information ofa plurality of terminals may be transmitted through the PUCCH and whencode division multiplexing (CDM) is performed to distinguish signals ofthe respective terminals, a constant amplitude zero autocorrelation(CAZAC) sequence having a length of 12 is primary used. Since the CAZACsequence has a characteristic to maintain a predetermined amplitude inthe time domain and the frequency domain, the CAZAC sequence has aproperty suitable for increasing coverage by decreasing apeak-to-average power ratio (PAPR) or cubic metric (CM) of the terminal.Further, the ACK/NACK information for downlink data transmissionperformed through the PUCCH is covered by using an orthogonal sequenceor an orthogonal cover (OC).

Further, the control information transmitted on the PUCCH may bedistinguished by using a cyclically shifted sequence having differentcyclic shift (CS) values. The cyclically shifted sequence may begenerated by cyclically shifting a base sequence by a specific cyclicshift (CS) amount. The specific CS amount is indicated by the cyclicshift (CS) index. The number of usable cyclic shifts may vary dependingon delay spread of the channel. Various types of sequences may be usedas the base sequence the CAZAC sequence is one example of thecorresponding sequence.

Further, the amount of control information which the terminal maytransmit in one subframe may be determined according to the number (thatis, SC-FDMA symbols other an SC-FDMA symbol used for transmitting areference signal (RS) for coherent detection of the PUCCH) of SC-FDMAsymbols which are usable for transmitting the control information.

In the 3GPP LTE system, the PUCCH is defined as a total of 7 differentformats according to the transmitted control information, a modulationtechnique, the amount of control information, and the like and anattribute of the uplink control information (UCI) transmitted accordingto each PUCCH format may be summarized as shown in Table 2 given below.

TABLE 2 PUCCH Format Uplink Control Information(UCI) Format 1 SchedulingRequest(SR) (unmodulated waveform) Format 1a 1-bit HARQ ACK/NACKwith/without SR Format 1b 2-bit HARQ ACK/NACK with/without SR Format 2CQI (20 coded bits) Format 2 CQI and 1- or 2-bit HARQ ACK/NACK (20 bits)for extended CP only Format 2a CQI and 1-bit HARQ ACK/NACK (20 + 1 codedbits) Format 2b CQI and 2-bit HARQ ACK/NACK (20 + 2 coded bits)

PUCCH format 1 is used for transmitting only the SR. A waveform which isnot modulated is adopted in the case of transmitting only the SR andthis will be described below in detail.

PUCCH format 1a or 1b is used for transmitting the HARQ ACK/NACK. PUCCHformat 1a or 1b may be used when only the HARQ ACK/NACK is transmittedin a predetermined subframe. Alternatively, the HARQ ACK/NACK and the SRmay be transmitted in the same subframe by using PUCCH format 1a or 1b.

PUCCH format 2 is used for transmitting the CQI and PUCCH format 2a or2b is used for transmitting the CQI and the HARQ ACK/NACK.

In the case of an extended CP, PUCCH format 2 may be transmitted fortransmitting the CQI and the HARQ ACK/NACK.

FIG. 5 illustrates one example of a type in which PUCCH formats aremapped to a PUCCH region of an uplink physical resource block in thewireless communication system to which the present invention can beapplied.

In FIG. 5, N_(RB) ^(UL) represents the number of resource blocks in theuplink and 0, 1, . . . , N_(RB) ^(UL)−1 mean numbers of physicalresource blocks. Basically, the PUCCH is mapped to both edges of anuplink frequency block. As illustrated in FIG. 5, PUCCH format 2/2a/2bis mapped to a PUCCH region expressed as m=0, 1 and this may beexpressed in such a manner that PUCCH format 2/2a/2b is mapped toresource blocks positioned at a band edge. Further, both PUCCH format2/2a/2b and PUCCH format 1/1a/1b may be mixedly mapped to a PUCCH regionexpressed as m=2. Next, PUCCH format 1/1a/1b may be mapped to a PUCCHregion expressed as m=3, 4, and 5. The number (N_(RB) ⁽²⁾) of PUCCH RBswhich are usable by PUCCH format 2/2a/2b may be indicated to terminalsin the cell by broadcasting signaling.

PUCCH format 2/2a/2b is described. PUCCH format 2/2a/2b is a controlchannel for transmitting channel measurement feedback (CQI, PMI, andRI).

A reporting period of the channel measurement feedbacks (hereinafter,collectively expressed as CQI information) and a frequency wise(alternatively, a frequency resolution) to be measured may be controlledby the base station. In the time domain, periodic and aperiodic CQIreporting may be supported. PUCCH format 2 may be used for only theperiodic reporting and the PUSCH may be used for aperiodic reporting. Inthe case of the aperiodic reporting, the base station may instruct theterminal to transmit a scheduling resource loaded with individual CQIreporting for the uplink data transmission.

FIG. 6 illustrates a structure of a CQI channel in the case of a generalCP in the wireless communication system to which the present inventioncan be applied.

In SC-FDMA symbols 0 to 6 of one slot, SC-FDMA symbols 1 and 5 (secondand sixth symbols) may be used for transmitting a demodulation referencesignal and the CQI information may be transmitted in the residualSC-FDMA symbols. Meanwhile, in the case of the extended CP, one SC-FDMAsymbol (SC-FDMA symbol 3) is used for transmitting the DMRS.

In PUCCH format 2/2a/2b, modulation by the CAZAC sequence is supportedand the CAZAC sequence having the length of 12 is multiplied by aQPSK-modulated symbol. The cyclic shift (CS) of the sequence is changedbetween the symbol and the slot. The orthogonal covering is used withrespect to the DMRS.

The reference signal (DMRS) is loaded on two SC-FDMA symbols separatedfrom each other by 3 SC-FDMA symbols among 7 SC-FDMA symbols included inone slot and the CQI information is loaded on 5 residual SC-FDMAsymbols. Two RSs are used in one slot in order to support a high-speedterminal. Further, the respective terminals are distinguished by usingthe CS sequence. CQI information symbols are modulated and transferredto all SC-FDMA symbols and the SC-FDMA symbol is constituted by onesequence. That is, the terminal modulates and transmits the CQI to eachsequence.

The number of symbols which may be transmitted to one TTI is 10 andmodulation of the CQI information is determined up to QPSK. When QPSKmapping is used for the SC-FDMA symbol, since a CQI value of 2 bits maybe loaded, a CQI value of 10 bits may be loaded on one slot. Therefore,a CQI value of a maximum of 20 bits may be loaded on one subframe. Afrequency domain spread code is used for spreading the CQI informationin the frequency domain.

The CAZAC sequence (for example, ZC sequence) having the length of 12may be used as the frequency domain spread code. CAZAC sequences havingdifferent CS values may be applied to the respective control channels tobe distinguished from each other. IFFT is performed with respect to theCQI information in which the frequency domain is spread.

12 different terminals may be orthogonally multiplexed on the same PUCCHRB by a cyclic shift having 12 equivalent intervals. In the case of ageneral CP, a DMRS sequence on SC-FDMA symbol 1 and 5 (on SC-FDMA symbol3 in the case of the extended CP) is similar to a CQI signal sequence onthe frequency domain, but the modulation of the CQI information is notadopted.

The terminal may be semi-statically configured by upper-layer signalingso as to periodically report different CQI, PMI, and RI types on PUCCHresources indicated as PUCCH resource indexes (n_(PUCCH)^((1,{tilde over (p)})), n_(PUCCH) ^((2,{tilde over (p)})), andn_(PUCCH) ^((3,{tilde over (p)}))). Herein, the PUCCH resource index(n_(PUCCH) ^((2,{tilde over (p)}))) is information indicating the PUCCHregion used for PUCCH format 2/2a/2b and a CS value to be used.

PUCCH Channel Structure

PUCCH formats 1a and 1b are described.

In PUCCH format 1a and 1b, the CAZAC sequence having the length of 12 ismultiplied by a symbol modulated by using a BPSK or QPSK modulationscheme. For example, a result acquired by multiplying a modulated symbold(0) by a CAZAC sequence r(n) (n=0, 1, 2, . . . , N−1) having a lengthof N becomes y(0), y(1), y(2), . . . , y(N−1). y(0), . . . , y(N−1)symbols may be designated as a block of symbols. The modulated symbol ismultiplied by the CAZAC sequence and thereafter, the block-wise spreadusing the orthogonal sequence is adopted.

A Hadamard sequence having a length of 4 is used with respect to generalACK/NACK information and a discrete Fourier transform (DFT) sequencehaving a length of 3 is used with respect to the ACK/NACK informationand the reference signal.

The Hadamard sequence having the length of 2 is used with respect to thereference signal in the case of the extended CP.

FIG. 7 illustrates a structure of an ACK/NACK channel in the case of ageneral CP in the wireless communication system to which the presentinvention can be applied.

In FIG. 7, a PUCCH channel structure for transmitting the HARQ ACK/NACKwithout the CQI is exemplarily illustrated.

The reference signal (DMRS) is loaded on three consecutive SC-FDMAsymbols in a middle part among 7 SC-FDMA symbols and the ACK/NACK signalis loaded on 4 residual SC-FDMA symbols.

Meanwhile, in the case of the extended CP, the RS may be loaded on twoconsecutive symbols in the middle part. The number of and the positionsof symbols used in the RS may vary depending on the control channel andthe numbers and the positions of symbols used in the ACK/NACK signalassociated with the positions of symbols used in the RS may alsocorrespondingly vary depending on the control channel.

Acknowledgment response information (not scrambled status) of 1 bit and2 bits may be expressed as one HARQ ACK/NACK modulated symbol by usingthe BPSK and QPSK modulation techniques, respectively. A positiveacknowledgement response (ACK) may be encoded as ‘1’ and a negativeacknowledgment response (NACK) may be encoded as ‘0’.

When a control signal is transmitted in an allocated band, 2-dimensional(D) spread is adopted in order to increase a multiplexing capacity. Thatis, frequency domain spread and time domain spread are simultaneouslyadopted in order to increase the number of terminals or control channelswhich may be multiplexed.

A frequency domain sequence is used as the base sequence in order tospread the ACK/NACK signal in the frequency domain. A Zadoff-Chu (ZC)sequence which is one of the CAZAC sequences may be used as thefrequency domain sequence. For example, different CSs are applied to theZC sequence which is the base sequence, and as a result, multiplexingdifferent terminals or different control channels may be applied. Thenumber of CS resources supported in an SC-FDMA symbol for PUCCH RBs forHARQ ACK/NACK transmission is set by a cell-specific upper-layersignaling parameter (Δ_(shift) ^(PUCCH)).

The ACK/NACK signal which is frequency-domain spread is spread in thetime domain by using an orthogonal spreading code. As the orthogonalspreading code, a Walsh-Hadamard sequence or DFT sequence may be used.For example, the ACK/NACK signal may be spread by using an orthogonalsequence (w0, w1, w2, and w3) having the length of 4 with respect to 4symbols. Further, the RS is also spread through an orthogonal sequencehaving the length of 3 or 2. This is referred to as orthogonal covering(OC).

Multiple terminals may be multiplexed by a code division multiplexing(CDM) scheme by using the CS resources in the frequency domain and theOC resources in the time domain described above. That is, ACK/NACKinformation and RSs of a lot of terminals may be multiplexed on the samePUCCH RB.

In respect to the time-domain spread CDM, the number of spreading codessupported with respect to the ACK/NACK information is limited by thenumber of RS symbols. That is, since the number of RS transmittingSC-FDMA symbols is smaller than that of ACK/NACK informationtransmitting SC-FDMA symbols, the multiplexing capacity of the RS issmaller than that of the ACK/NACK information.

For example, in the case of the general CP, the ACK/NACK information maybe transmitted in four symbols and not 4 but 3 orthogonal spreadingcodes are used for the ACK/NACK information and the reason is that thenumber of RS transmitting symbols is limited to 3 to use only 3orthogonal spreading codes for the RS.

In the case of the subframe of the general CP, when 3 symbols are usedfor transmitting the RS and 4 symbols are used for transmitting theACK/NACK information in one slot, for example, if 6 CSs in the frequencydomain and 3 orthogonal cover (OC) resources may be used, HARQacknowledgement responses from a total of 18 different terminals may bemultiplexed in one PUCCH RB. In the case of the subframe of the extendedCP, when 2 symbols are used for transmitting the RS and 4 symbols areused for transmitting the ACK/NACK information in one slot, for example,if 6 CSs in the frequency domain and 2 orthogonal cover (OC) resourcesmay be used, the HARQ acknowledgement responses from a total of 12different terminals may be multiplexed in one PUCCH RB.

Next, PUCCH format 1 is described. The scheduling request (SR) istransmitted by a scheme in which the terminal requests scheduling ordoes not request the scheduling. An SR channel reuses an ACK/NACKchannel structure in PUCCH format 1a/1b and is configured by an on-offkeying (OOK) scheme based on an ACK/NACK channel design. In the SRchannel, the reference signal is not transmitted. Therefore, in the caseof the general CP, a sequence having a length of 7 is used and in thecase of the extended CP, a sequence having a length of 6 is used.Different cyclic shifts (CSs) or orthogonal covers (OCs) may beallocated to the SR and the ACK/NACK. That is, the terminal transmitsthe HARQ ACK/NACK through a resource allocated for the SR in order totransmit a positive SR. The terminal transmits the HARQ ACK/NACK througha resource allocated for the ACK/NACK in order to transmit a negativeSR.

Next, an enhanced-PUCCH (e-PUCCH) format is described. An e-PUCCH maycorrespond to PUCCH format 3 of an LTE-A system. A block spreadingtechnique may be applied to ACK/NACK transmission using PUCCH format 3.

The block spreading technique is a scheme that modulates transmission ofthe control signal by using the SC-FDMA scheme unlike the existing PUCCHformat 1 series or 2 series. As illustrated in FIG. 8, a symbol sequencemay be spread and transmitted on the time domain by using an orthogonalcover code (OCC). The control signals of the plurality of terminals maybe multiplexed on the same RB by using the OCC. In the case of PUCCHformat 2 described above, one symbol sequence is transmitted throughoutthe time domain and the control signals of the plurality of terminalsare multiplexed by using the cyclic shift (CS) of the CAZAC sequence,while in the case of a block spreading based on PUCCH format (forexample, PUCCH format 3), one symbol sequence is transmitted throughoutthe frequency domain and the control signals of the plurality ofterminals are multiplexed by using the time domain spreading using theOCC.

FIG. 8 illustrates one example of generating and transmitting 5 SC-FDMAsymbols during one slot in the wireless communication system to whichthe present invention can be applied.

In FIG. 8, an example of generating and transmitting 5 SC-FDMA symbols(that is, data part) by using an OCC having the length of 5(alternatively, SF=5) in one symbol sequence during one slot. In thiscase, two RS symbols may be used during one slot.

In the example of FIG. 8, the RS symbol may be generated from a CAZACsequence to which a specific cyclic shift value is applied andtransmitted in a type in which a predetermined OCC is applied(alternatively, multiplied) throughout a plurality of RS symbols.Further, in the example of FIG. 8, when it is assumed that 12 modulatedsymbols are used for each OFDM symbol (alternatively, SC-FDMA symbol)and the respective modulated symbols are generated by QPSK, the maximumbit number which may be transmitted in one slot becomes 24 bits (=12×2).Accordingly, the bit number which is transmittable by two slots becomesa total of 48 bits. When a PUCCH channel structure of the blockspreading scheme is used, control information having an extended sizemay be transmitted as compared with the existing PUCCH format 1 seriesand 2 series.

General Carrier Aggregation

A communication environment considered in embodiments of the presentinvention includes multi-carrier supporting environments. That is, amulti-carrier system or a carrier aggregation system used in the presentinvention means a system that aggregates and uses one or more componentcarriers (CCs) having a smaller bandwidth smaller than a target band atthe time of configuring a target wideband in order to support awideband.

In the present invention, multi-carriers mean aggregation of(alternatively, carrier aggregation) of carriers and in this case, theaggregation of the carriers means both aggregation between continuouscarriers and aggregation between non-contiguous carriers. Further, thenumber of component carriers aggregated between the downlink and theuplink may be differently set. A case in which the number of downlinkcomponent carriers (hereinafter, referred to as ‘DL CC’) and the numberof uplink component carriers (hereinafter, referred to as ‘UL CC’) arethe same as each other is referred to as symmetric aggregation and acase in which the number of downlink component carriers and the numberof uplink component carriers are different from each other is referredto as asymmetric aggregation. The carrier aggregation may be usedmixedly with a term such as the carrier aggregation, the bandwidthaggregation, spectrum aggregation, or the like.

The carrier aggregation configured by combining two or more componentcarriers aims at supporting up to a bandwidth of 100 MHz in the LTE-Asystem. When one or more carriers having the bandwidth than the targetband are combined, the bandwidth of the carriers to be combined may belimited to a bandwidth used in the existing system in order to maintainbackward compatibility with the existing IMT system. For example, theexisting 3GPP LTE system supports bandwidths of 1.4, 3, 5, 10, 15, and20 MHz and a 3GPP LIE-advanced system (that is, LTE-A) may be configuredto support a bandwidth larger than 20 MHz by using on the bandwidth forcompatibility with the existing system. Further, the carrier aggregationsystem used in the preset invention may be configured to support thecarrier aggregation by defining a new bandwidth regardless of thebandwidth used in the existing system.

The LTE-A system uses a concept of the cell in order to manage a radioresource.

The carrier aggregation environment may be called a multi-cellenvironment. The cell is defined as a combination of a pair of adownlink resource (DL CC) and an uplink resource (UL CC), but the uplinkresource is not required. Therefore, the cell may be constituted by onlythe downlink resource or both the downlink resource and the uplinkresource. When a specific terminal has only one configured serving cell,the cell may have one DL CC and one UL CC, but when the specificterminal has two or more configured serving cells, the cell has DL CCsas many as the cells and the number of UL CCs may be equal to or smallerthan the number of DL CCs.

Alternatively, contrary to this, the DL CC and the UL CC may beconfigured. That is, when the specific terminal has multiple configuredserving cells, a carrier aggregation environment having UL CCs more thanDL CCs may also be supported. That is, the carrier aggregation may beappreciated as aggregation of two or more cells having different carrierfrequencies (center frequencies). Herein, the described ‘cell’ needs tobe distinguished from a cell as an area covered by the base stationwhich is generally used.

The cell used in the LTE-A system includes a primary cell (PCell) and asecondary cell (SCell. The P cell and the S cell may be used as theserving cell. In a terminal which is in an RRC_CONNECTED state, but doesnot have the configured carrier aggregation or does not support thecarrier aggregation, only one serving constituted by only the P cell ispresent. On the contrary, in a terminal which is in the RRC_CONNECTEDstate and has the configured carrier aggregation, one or more servingcells may be present and the P cell and one or more S cells are includedin all serving cells.

The serving cell (P cell and S cell) may be configured through an RRCparameter. PhysCellId as a physical layer identifier of the cell hasinteger values of 0 to 503. SCellIndex as a short identifier used toidentify the S cell has integer values of 1 to 7. ServCellIndex as ashort identifier used to identify the serving cell (P cell or S cell)has the integer values of 0 to 7. The value of 0 is applied to the Pcell and SCellIndex is previously granted for application to the S cell.That is, a cell having a smallest cell ID (alternatively, cell index) inServCellIndex becomes the P cell.

The P cell means a cell that operates on a primary frequency(alternatively, primary CC). The terminal may be used to perform aninitial connection establishment process or a connectionre-establishment process and may be designated as a cell indicatedduring a handover process. Further, the P cell means a cell whichbecomes the center of control associated communication among servingcells configured in the carrier aggregation environment. That is, theterminal may be allocated with and transmit the PUCCH only in the P cellthereof and use only the P cell to acquire the system information orchange a monitoring procedure. An evolved universal terrestrial radioaccess (E-UTRAN) may change only the P cell for the handover procedureto the terminal supporting the carrier aggregation environment by usingan RRC connection reconfiguration message (RRCConnectionReconfigutaion)message of an upper layer including mobile control information(mobilityControlInfo).

The S cell means a cell that operates on a secondary frequency(alternatively, secondary CC). Only one P cell may be allocated to aspecific terminal and one or more S cells may be allocated to thespecific terminal. The S cell may be configured after RRC connectionestablishment is achieved and used for providing an additional radioresource. The PUCCH is not present in residual cells other than the Pcell, that is, the S cells among the serving cells configured in thecarrier aggregation environment. The E-UTRAN may provide all systeminformation associated with a related cell which is in an RRC_CONNECTEDstate through a dedicated signal at the time of adding the S cells tothe terminal that supports the carrier aggregation environment. A changeof the system information may be controlled by releasing and adding therelated S cell and in this case, the RRC connection reconfiguration(RRCConnectionReconfigutaion) message of the upper layer may be used.The E-UTRAN may perform having different parameters for each terminalrather than broadcasting in the related S cell.

After an initial security activation process starts, the E-UTRAN addsthe S cells to the P cell initially configured during the connectionestablishment process to configure a network including one or more Scells. In the carrier aggregation environment, the P cell and the S cellmay operate as the respective component carriers. In an embodimentdescribed below, the primary component carrier (PCC) may be used as thesame meaning as the P cell and the secondary component carrier (SCC) maybe used as the same meaning as the S cell.

FIG. 9 illustrates examples of a component carrier and carrieraggregation in the wireless communication system to which the presentinvention can be applied.

FIG. 9a illustrates a single carrier structure used in an LTE system.The component carrier includes the DL CC and the UL CC. One componentcarrier may have a frequency range of 20 MHz.

FIG. 9b illustrates a carrier aggregation structure used in the LTEsystem. In the case of FIG. 9b , a case is illustrated, in which threecomponent carriers having a frequency magnitude of 20 MHz are combined.Each of three DL CCs and three UL CCs is provided, but the number of DLCCs and the number of UL CCs are not limited. In the case of carrieraggregation, the terminal may simultaneously monitor three CCs, andreceive downlink signal/data and transmit uplink signal/data.

When N DL CCs are managed in a specific cell, the network may allocate M(M≤N) DL CCs to the terminal. In this case, the terminal may monitoronly M limited DL CCs and receive the DL signal. Further, the networkgives L (L≤M≤N) DL CCs to allocate a primary DL CC to the terminal andin this case, UE needs to particularly monitor L DL CCs. Such a schememay be similarly applied even to uplink transmission.

A linkage between a carrier frequency (alternatively, DL CC) of thedownlink resource and a carrier frequency (alternatively, UL CC) of theuplink resource may be indicated by an upper-layer message such as theRRC message or the system information. For example, a combination of theDL resource and the UL resource may be configured by a linkage definedby system information block type 2 (SIB2). In detail, the linkage maymean a mapping relationship between the DL CC in which the PDCCHtransporting a UL grant and a UL CC using the UL grant and mean amapping relationship between the DL CC (alternatively, UL CC) in whichdata for the HARQ is transmitted and the UL CC (alternatively, DL CC) inwhich the HARQ ACK/NACK signal is transmitted.

Cross Carrier Scheduling

In the carrier aggregation system, in terms of scheduling for thecarrier or the serving cell, two types of a self-scheduling method and across carrier scheduling method are provided. The cross carrierscheduling may be called cross component carrier scheduling or crosscell scheduling.

The cross carrier scheduling means transmitting the PDCCH (DL grant) andthe PDSCH to different respective DL CCs or transmitting the PUSCHtransmitted according to the PDCCH (UL grant) transmitted in the DL CCthrough other UL CC other than a UL CC linked with the DL CC receivingthe UL grant.

Whether to perform the cross carrier scheduling may be UE-specificallyactivated or deactivated and semi-statically known for each terminalthrough the upper-layer signaling (for example, RRC signaling).

When the cross carrier scheduling is activated, a carrier indicatorfield (CIF) indicating through which DL/UL CC the PDSCH/PUSCH thePDSCH/PUSCH indicated by the corresponding PDCCH is transmitted isrequired. For example, the PDCCH may allocate the PDSCH resource or thePUSCH resource to one of multiple component carriers by using the CIF.That is, the CIF is set when the PDSCH or PUSCH resource is allocated toone of DL/UL CCs in which the PDCCH on the DL CC is multiply aggregated.In this case, a DCI format of LTE-A Release-8 may extend according tothe CIF. In this case, the set CIF may be fixed to a 3-bit field and theposition of the set CIF may be fixed regardless of the size of the DCIformat. Further, a PDCCH structure (the same coding and the same CCEbased resource mapping) of the LTE-A Release-8 may be reused.

On the contrary, when the PDCCH on the DL CC allocates the PDSCHresource on the same DL CC or allocates the PUSCH resource on a UL CCwhich is singly linked, the CIF is not set. In this case, the same PDCCHstructure (the same coding and the same CCE based resource mapping) andDCI format as the LTE-A Release-8 may be used.

When the cross carrier scheduling is possible, the terminal needs tomonitor PDCCHs for a plurality of DCIs in a control region of amonitoring CC according to a transmission mode and/or a bandwidth foreach CC. Therefore, a configuration and PDCCH monitoring of a searchspace which may support monitoring the PDCCHs for the plurality of DCIsare required.

In the carrier aggregation system, a terminal DL CC aggregate representsan aggregate of DL CCs in which the terminal is scheduled to receive thePDSCH and a terminal UL CC aggregate represents an aggregate of UL CCsin which the terminal is scheduled to transmit the PUSCH. Further, aPDCCH monitoring set represents a set of one or more DL CCs that performthe PDCCH monitoring. The PDCCH monitoring set may be the same as theterminal DL CC set or a subset of the terminal DL CC set. The PDCCHmonitoring set may include at least any one of DL CCs in the terminal DLCC set. Alternatively, the PDCCH monitoring set may be definedseparately regardless of the terminal DL CC set. The DL CCs included inthe PDCCH monitoring set may be configured in such a manner thatself-scheduling for the linked UL CC is continuously available. Theterminal DL CC set, the terminal UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

When the cross carrier scheduling is deactivated, the deactivation ofthe cross carrier scheduling means that the PDCCH monitoring setcontinuously means the terminal DL CC set and in this case, anindication such as separate signaling for the PDCCH monitoring set isnot required. However, when the cross carrier scheduling is activated,the PDCCH monitoring set is preferably defined in the terminal DL CCset. That is, the base station transmits the PDCCH through only thePDCCH monitoring set in order to schedule the PDSCH or PUSCH for theterminal.

FIG. 10 illustrates one example of a subframe structure depending oncross carrier scheduling in the wireless communication system to whichthe present invention can be applied.

Referring to FIG. 10, a case is illustrated, in which three DL CCs areassociated with a DL subframe for an LTE-A terminal and DL CC′A′ isconfigured as a PDCCH monitoring DL CC. When the CIF is not used, eachDL CC may transmit the PDCCH scheduling the PDSCH thereof without theCIF. On the contrary, when the CIF is used through the upper-layersignaling, only one DL CC ‘A’ may transmit the PDCCH scheduling thePDSCH thereof or the PDSCH of another CC by using the CIF. In this case,DL CC ‘B’ and ‘C’ in which the PDCCH monitoring DL CC is not configureddoes not transmit the PDCCH.

General ACK/NACK Multiplexing Method

In a situation in which the terminal simultaneously needs to transmitmultiple ACKs/NACKs corresponding to multiple data units received froman eNB, an ACK/NACK multiplexing method based on PUCCH resourceselection may be considered in order to maintain a single-frequencycharacteristic of the ACK/NACK signal and reduce ACK/NACK transmissionpower.

Together with ACK/NACK multiplexing, contents of ACK/NACK responses formultiple data units may be identified by combining a PUCCH resource anda resource of QPSK modulation symbols used for actual ACK/NACKtransmission.

For example, when one PUCCH resource may transmit 4 bits and four dataunits may be maximally transmitted, an ACK/NACK result may be identifiedin the eNB as shown in Table 3 given below.

TABLE 3 HARQ-ACK(0), HARQ-ACK(1), HARQ-ACK(2), HARQ-ACK(3) n_(PUCCH) ⁽¹⁾b(0), b(1) ACK, ACK, ACK, ACK n_(PUCCH, 1) ⁽¹⁾ 1, 1 ACK, ACK, ACK,NACK/DTX n_(PUCCH, 1) ⁽¹⁾ 1, 0 NACK/DTX, NACK/DTX, NACK, DTXn_(PUCCH, 2) ⁽¹⁾ 1, 1 ACK, ACK, NACK/DTX, ACK n_(PUCCH, 1) ⁽¹⁾ 1, 0NACK, DTX, DTX, DTX n_(PUCCH, 0) ⁽¹⁾ 1, 0 ACK, ACK, NACK/DTX, NACK/DTXn_(PUCCH, 1) ⁽¹⁾ 1, 0 ACK, NACK/DTX, ACK, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 1NACK/DTX, NACK/DTX, NACK/DTX, n_(PUCCH, 3) ⁽¹⁾ 1, 1 NACK ACK, NACK/DTX,ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, ACKn_(PUCCH, 0) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, NACK/DTX n_(PUCCH, 0) ⁽¹⁾1, 1 NACK/DTX, ACK, ACK, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 1 NACK/DTX, NACK, DTX,DTX n_(PUCCH, 1) ⁽¹⁾ 0, 0 NACK/DTX, ACK, ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾1, 0 NACK/DTX, ACK, NACK/DTX, ACK n_(PUCCH, 3) ⁽¹⁾ 1, 0 NACK/DTX, ACK,NACK/DTX, NACK/DTX n_(PUCCH, 1) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, ACKn_(PUCCH, 3) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾0, 0 NACK/DTX, NACK/DTX, NACK/DTX, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 0 DTX, DTX,DTX, DTX N/A N/A

In Table 3 given above, HARQ-ACK(i) represents an ACK/NACK result for ani-th data unit. In Table 3 given above, discontinuous transmission (DTX)means that there is no data unit to be transmitted for the correspondingHARQ-ACK(i) or that the terminal may not detect the data unitcorresponding to the HARQ-ACK(i).

According to Table 3 given above, a maximum of four PUCCH resources(n_(PUCCH,0) ⁽¹⁾, n_(PUCCH,1) ⁽¹⁾, n_(PUCCH,2) ⁽¹⁾, and n_(PUCCH,3) ⁽¹⁾)are provided and b(0) and b(1) are two bits transmitted by using aselected PUCCH.

For example, when the terminal successfully receives all of four dataunits, the terminal transmits 2 bits (1,1) by using n_(PUCCH,1) ⁽¹⁾.

When the terminal fails to decoding in first and third data units andsucceeds in decoding in second and fourth data units, the terminaltransmits bits (1,0) by using n_(PUCCH,3) ⁽¹⁾.

In ACK/NACK channel selection, when there is at least one ACK, the NACKand the DTX are coupled with each other. The reason is that acombination of the PUCCH resource and the QPSK symbol may not allACK/NACK states. However, when there is no ACK, the DTX is decoupledfrom the NACK.

In this case, the PUCCH resource linked to the data unit correspondingto one definite NACK may also be reserved to transmit signals ofmultiple ACKs/NACKs.

Validation of PDCCH for Semi-Persistent Scheduling

Semi-persistent scheduling (SPS) is a scheduling scheme that allocatesthe resource to the terminal to be persistently maintained during aspecific time interval.

When a predetermined amount of data is transmitted for a specific timelike a voice over Internet protocol (VoIP), since the controlinformation need not be transmitted every data transmission interval forthe resource allocation, the waste of the control information may bereduced by using the SPS scheme. In a so-called semi-persistentscheduling (SPS) method, a time resource domain in which the resourcemay be allocated to the terminal is preferentially allocated.

In this case, in a semi-persistent allocation method, a time resourcedomain allocated to a specific terminal may be configured to haveperiodicity. Then, a frequency resource domain is allocated as necessaryto complete allocation of the time-frequency resource. Allocating thefrequency resource domain may be designated as so-called activation.When the semi-persistent allocation method is used, since the resourceallocation is maintained during a predetermined period by one-timesignaling, the resource need not be repeatedly allocated, and as aresult, signaling overhead may be reduced.

Thereafter, since the resource allocation to the terminal is notrequired, signaling for releasing the frequency resource allocation maybe transmitted from the base station to the terminal. Releasing theallocation of the frequency resource domain may be designated asdeactivation.

In current LTE, in which subframes the SPS is first transmitted/receivedthrough radio resource control (RRC) signaling for the SPS for theuplink and/or downlink is announced to the terminal. That is, the timeresource is preferentially designated among the time and frequencyresources allocated for the SPS through the RRC signaling. In order toannounce a usable subframe, for example, a period and an offset of thesubframe may be announced. However, since the terminal is allocated withonly the time resource domain through the RRC signaling, even though theterminal receives the RRC signaling, the terminal does not immediatelyperform transmission and reception by the SPS and the terminal allocatesthe frequency resource domain as necessary to complete the allocation ofthe time-frequency resource. Allocating the frequency resource domainmay be designated as deactivation and releasing the allocation of thefrequency resource domain may be designated as deactivation.

Therefore, the terminal receives the PDCCH indicating the activation andthereafter, allocate the frequency resource according to RB allocationinformation included in the received PDCCH and applies modulation andcode rate depending on modulation and coding scheme (MCS) information tostart transmission and reception according to the period and the offsetof the subframe allocated through the RRC signaling.

Next, when the terminal receives the PDCCH announcing the deactivationfrom the base station, the terminal stops transmission and reception.When the terminal receives the PDCCH indicating the activation orreactivation after stopping the transmission and reception, the terminalresumes the transmission and reception again with the period and theoffset of the subframe allocated through the RRC signaling by using theRC allocation, the MCS, and the like designated by the PDCCH. That is,the time resource is performed through the RRC signaling, but the signalmay be actually transmitted and received after receiving the PDCCHindicating the activation and reactivation of the SPS and the signaltransmission and reception stop after receiving the PDCCH indicating thedeactivation of the SPS.

When all conditions described below are satisfied, the terminal mayvalidate a PDCCH including an SPS indication. First, a CRC parity bitadded for a PDCCH payload needs to be scrambled with an SPS C-RNTI andsecond, a new data indicator (NDI) field needs to be set to 0. Herein,in the case of DCI formats 2, 2A, 2B, and 2C, the new data indicatorfield indicates one activated transmission block.

In addition, when each field used in the DCI format is set according toTables 4 and 5 given below, the validation is completed. When thevalidation is completed, the terminal recognizes that received DCIinformation is valid SPS activation or deactivation (alternatively,release). On the contrary, when the validation is not completed, theterminal recognizes that a non-matching CRC is included in the receivedDCI format.

Table 4 shows a field for validating the PDCCH indicating the SPSactivation.

TABLE 4 DCI format DCI format DCI format 0 1/1A 2/2A/2B TPC command forset to N/A N/A scheduled PUSCH ‘00’ Cyclic shift DM RS set to N/A N/A‘000’ Modulation and MSB is N/A N/A coding scheme and set to redundancyversion ‘0’ HARQ process number N/A FDD: set FDD: set to ‘000’ to ‘000’TDD: set TDD: set to ‘0000’ to ‘0000’ Modulation and N/A MSB is For theenabled coding scheme set to transport block: ‘0’ MSB is set to ‘0’Redundancy version N/A set to For the enabled ‘00’ transport block: setto ‘00’

Table 5 shows a field for validating the PDCCH indicating the SPSdeactivation (alternatively, release).

TABLE 5 DCI format DCI format 0 1A TPC command for set to N/A scheduledPUSCH ‘00’ Cyclic shift DM RS set to N/A ‘000’ Modulation and set to N/Acoding scheme and ‘11111’ redundancy version Resource block Set to N/Aassignment and all ‘1’s hopping resource allocation HARQ process numberN/A FDD: set to ‘000’ TDD: set to ‘0000’ Modulation and N/A set tocoding scheme ‘11111’ Redundancy version N/A set to ‘00’ Resource blockN/A Set to assignment all ‘1’s

When the DCI format indicates SPS downlink scheduling activation, a TPCcommand value for the PUCCH field may be used as indexes indicating fourPUCCH resource values set by the upper layer.

PUCCH Piggybacking in Rel-8 LTE

FIG. 11 illustrates one example of transport channel processing of aUL-SCH in the wireless communication system to which the presentinvention can be applied.

In a 3GPP LTE system (=E-UTRA, Rel. 8), in the case of the UL, singlecarrier transmission having an excellent peak-to-average power ratio(PAPR) or cubic metric (CM) characteristic which influences theperformance of a power amplifier is maintained for efficient utilizationof the power amplifier of the terminal. That is, in the case oftransmitting the PUSCH of the existing LTE system, data to betransmitted may maintain the single carrier characteristic throughDFT-precoding and in the case of transmitting the PUCCH, information istransmitted while being loaded on a sequence having the single carriercharacteristic to maintain the single carrier characteristic. However,when the data to be DFT-precoded is non-contiguously allocated to afrequency axis or the PUSCH and the PUCCH are simultaneouslytransmitted, the single carrier characteristic deteriorates. Therefore,when the PUSCH is transmitted in the same subframe as the transmissionof the PUCCH as illustrated in FIG. 11, uplink control information (UCI)to be transmitted to the PUCCH is transmitted (piggyback) together withdata through the PUSCH.

Since the PUCCH and the PUSCH may not be simultaneously transmitted asdescribed above, the existing LTE terminal uses a method thatmultiplexes uplink control information (UCI) (CQI/PMI, HARQ-ACK, RI, andthe like) to the PUSCH region in a subframe in which the PUSCH istransmitted.

As one example, when the channel quality indicator (CQI) and/orprecoding matrix indicator (PMI) needs to be transmitted in a subframeallocated to transmit the PUSCH, UL-SCH data and the CQI/PMI aremultiplexed after DFT-spreading to transmit both control information anddata. In this case, the UL-SCH data is rate-matched by considering aCQI/PMI resource. Further, a scheme is used, in which the controlinformation such as the HARQ ACK, the RI, and the like punctures theUL-SCH data to be multiplexed to the PUSCH region.

FIG. 12 illustrates one example of a signal processing process of anuplink share channel of a transport channel in the wirelesscommunication system to which the present invention can be applied.

Herein, the signal processing process of the uplink share channel(hereinafter, referred to as “UL-SCH”) may be applied to one or moretransport channels or control information types.

Referring to FIG. 12, the UL-SCH transfers data to a coding unit in theform of a transport block (TB) once every a transmission time interval(TTI).

A CRC parity bit p₀, p₁, p₂, p₃, . . . , p_(L−1) attached to a bit ofthe transport block received from the upper layer (S120). In this case,A represents the size of the transport block and L represents the numberof parity bits. Input bits to which the CRC is attached are shown in b₀,b₁, b₂, b₃, . . . , b_(B−1). In this case, B represents the number ofbits of the transport block including the CRC.

b₀, b₁, b₂, b₃, . . . , b_(B−1) is segmented into multiple code blocks(CBs) according to the size of the TB and the CRC is attached tomultiple segmented CBs (S121). Bits after the code block segmentationand the CRC attachment are shown in c_(r0), c_(r1), c_(r2), c_(r3), . .. , c_(r(K) _(r) ⁻¹⁾. Herein, r represents No. (r=0, . . . , C−1) of thecode block and K_(r) represents the bit number depending on the codeblock r. Further, C represents the total number of code blocks.

Subsequently, channel coding is performed (S122). Output bits after thechannel coding are shown in d_(r0) ^((i)), d_(r1) ^((i)), d_(r2) ^((i)),d_(r3) ^((i)), . . . , d_(r(D) _(r) ⁻¹⁾ ^((i)). In this case, irepresents an encoded stream index and may have a value of 0, 1, or 2.D_(r) represents the number of bits of the i-th encoded stream for thecode block r. r represents the code block number (r=0, . . . , C−1) andC represents the total number of code blocks. Each code block may beencoded by turbo coding.

Subsequently, rate matching is performed (S123). Bits after the ratematching are shown in e_(r0), e_(r1), e_(r2), e_(r3), . . . , e_(r(E)_(r) ⁻¹⁾. In this case, r represents the code block number (r=0, . . . ,C−1) and C represents the total number of code blocks. E_(r) representsthe number of rate-matched bits of the r-th code block.

Subsequently, concatenation among the code blocks is performed again(S124). Bits after the concatenation of the code blocks is performed areshown in f₀, f₁, f₂, f₃, . . . , f_(G−1). In this case, G represents thetotal number of bits encoded for transmission and when the controlinformation is multiplexed with the UL-SCH, the number of bits used fortransmitting the control information is not included.

Meanwhile, when the control information is transmitted in the PUSCH,channel coding of the CQI/PMI, the RI, and the ACK/NACK which are thecontrol information is independently performed (S126, S127, and S128).Since different encoded symbols are allocated for transmitting eachcontrol information, the respective control information has differentcoding rates.

In time division duplex (TDD), as an ACK/NACK feedback mode, two modesof ACK/NACK bundling and ACK/NACK multiplexing are supported by anupper-layer configuration. ACK/NACK information bits for the ACK/NACKbundling are constituted by 1 bit or 2 bits and ACK/NACK informationbits for the ACK/NACK multiplexing are constituted by 1 to 4 bits.

After the concatenation among the code blocks in step S134, encoded bitsf₀, f₁, f₂, f₃, . . . , f_(G−1) of the UL-SCH data and encoded bits q₀,q₁, q₂, q₃, . . . , q_(N) _(L) _(·Q) _(CQI) ⁻¹ of the CQI/PMI aremultiplexed (S125). A multiplexed result of the data and the CQI/PMI isshown in g ₀, g ₁, g ₂, g ₃, . . . , g _(H′−1). In this case, g _(i)(i=0, . . . , H′−1) represents a column vector having a length of(Q_(m)·N_(L)). H=(G+N_(L)·Q_(CQI)) and H′=H/(N_(L)·Q_(m)). N_(L)represents the number of layers mapped to a UL-SCH transport block and Hrepresents the total number of encoded bits allocated to N_(L) transportlayers mapped with the transport block for the UL-SCH data and theCQI/PMI information.

Subsequently, the multiplexed data and CQI/PMI, a channel encoded RI,and the ACK/NACK are channel-interleaved to generate an output signal(S129).

Multi-Input Multi-Output (MIMO)

An MIMO technology uses multiple transmitting (Tx) antennas and multiplereceiving (Rx) antennas by breaking from generally one transmittingantenna and one receiving antenna up to now. In other words, the MIMOtechnology is a technology for achieving capacity increment orcapability enhancement by using a multiple input multiple output antennaat a transmitter side or a receiver side of the wireless communicationsystem. Hereinafter, “MIMO” will be referred to as “multiple inputmultiple output antenna”.

In more detail, the MIMO technology does not depend on one antenna pathin order to receive one total message and completes total data bycollecting a plurality of data pieces received through multipleantennas. Consequently, the MIMO technology may increase a data transferrate within in a specific system range and further, increase the systemrange through a specific data transfer rate.

In next-generation mobile communication, since a still higher datatransfer rate than the existing mobile communication is required, it isanticipated that an efficient multiple input multiple output technologyis particularly required. In such a situation, an MIMO communicationtechnology is a next-generation mobile communication technology whichmay be widely used in a mobile communication terminal and a relay andattracts a concern as a technology to overcome a limit of a transmissionamount of another mobile communication according to a limit situationdue to data communication extension, and the like.

Meanwhile, the multiple input multiple output (MIMO) technology amongvarious transmission efficiency improvement technologies which have beenresearched in recent years as a method that may epochally improve acommunication capacity and transmission and reception performancewithout additional frequency allocation or power increment has thelargest attention in recent years.

FIG. 13 is a configuration diagram of a general multiple input multipleoutput (MIMO) communication system.

Referring to FIG. 13, when the number of transmitting antennas increasesto N_(T) and the number of receiving antennas increases to N_(R) at thesame time, since a theoretical channel transmission capacity increasesin proportion to the number of antennas unlike a case using multipleantennas only in a transmitter or a receiver, a transfer rate may beimproved and frequency efficiency may be epchally improved. In thiscase, the transfer rate depending on an increase in channel transmissioncapacity may theoretically increase to a value acquired by multiplying amaximum transfer rate (R_(o)) in the case using one antenna by a rateincrease rate (R_(i)) given below.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, for example, in an MIMO communication system using fourtransmitting antennas and four receiving antennas, a transfer rate whichis four times higher than a single antenna system may be acquired.

Such an MIMO antenna technology may be divided into a spatial diversityscheme increasing transmission reliability by using symbols passingthrough various channel paths and a spatial multiplexing schemeimproving the transfer rate by simultaneously transmitting multiple datasymbols by using multiple transmitting antennas. Further, a researchinto a scheme that intends to appropriately acquire respectiveadvantages by appropriately combining two schemes is also a field whichhas been researched in recent years.

The respective schemes will be described below in more detail.

First, the spatial diversity scheme includes a space-time block codingseries and a space-time Trelis coding series scheme simultaneously usinga diversity gain and a coding gain. In general, the Trelis is excellentin bit error rate enhancement performance and code generation degree offreedom, but the space-time block code is simple in operationalcomplexity. In the case of such a spatial diversity gain, an amountcorresponding to a multiple (NT×NR) of the number (NT) of transmittingantennas and the number (NR) of receiving antennas may be acquired.

Second, the spatial multiplexing technique is a method that transmitsdifferent data arrays in the respective transmitting antennas and inthis case, mutual interference occurs among data simultaneouslytransmitted from the transmitter in the receiver. The receiver receivesthe data after removing the interference by using an appropriate signalprocessing technique. A noise removing scheme used herein includes amaximum likelihood detection (MLD) receiver, a zero-forcing (ZF)receiver, a minimum mean square error (MMSE) receiver, a diagonal-belllaboratories layered space-time (D-BLAST), a vertical-bell laboratorieslayered space-time), and the like and in particular, when channelinformation may be known in the transmitter side, a singular valuedecomposition (SVD) scheme, and the like may be used.

Third, a technique combining the space diversity and the spatialmultiplexing may be provided. When only the spatial diversity gain isacquired, the performance enhancement gain depending on an increase indiversity degree is gradually saturated and when only the spatialmultiplexing gain is acquired, the transmission reliability deterioratesin the radio channel. Schemes that acquire both two gains while solvingthe problem have been researched and the schemes include a space-timeblock code (Double-STTD), a space-time BICM (STBICM), and the like.

In order to describe a communication method in the MIMO antenna systemdescribed above by a more detailed method, when the communication methodis mathematically modeled, the mathematical modeling may be shown asbelow.

First, it is assumed that N_(T) transmitting antennas and N_(R)receiving antennas are present as illustrated in FIG. 13.

First, in respect to a transmission signal, when N_(T) transmittingantennas are provided, since the maximum number of transmittableinformation is N_(T), N_(T) may be expressed as a vector given below.s=[s ₁ ,s ₂ , . . . ,s _(N) _(T) ]^(T)  [Equation 2]

Meanwhile, transmission power may be different in the respectivetransmission information s₁, s₂, . . . , s_(NT) and in this case, whenthe respective transmission power is P₁, P₂, . . . , P_(NT), thetransmission information of which the transmission power is adjusted maybe expressed as a vector given below.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T)=[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P _(N)_(T) s _(N) _(T) ]^(T)  [Equation 3]

Further, ŝ may be expressed as described below as a diagonal matrix P ofthe transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

Meanwhile, the information vector ŝ of which the transmission power isadjusted is multiplied by a weight matrix W to constitute N_(T)transmission signals x₁, x₂, . . . , x_(NT) which are actuallytransmitted. Herein, the weight matrix serves to appropriatelydistribute the transmission information to the respective antennasaccording to a transmission channel situation, and the like. Thetransmission signals x₁, x₂, . . . , x_(NT) may be expressed as below byusing a vector x.

$\begin{matrix}{x = {\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{matrix} \rbrack = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

Herein, w_(ij) represents a weight between the i-th transmitting antennaand j-th transmission information and W represents the weight as thematrix. The matrix W is called a weight matrix or a precoding matrix.

Meanwhile, the transmission signal x described above may be divided intotransmission signals in a case using the spatial diversity and a caseusing the spatial multiplexing.

In the case using the spatial multiplexing, since different signals aremultiplexed and sent, all elements of an information vector s havedifferent values, while when the spatial diversity is used, since thesame signal is sent through multiple channel paths, all of the elementsof the information vector s have the same value.

Of course, a method mixing the spatial multiplexing and the spatialdiversity may also be considered. That is, for example, a case may alsobe considered, which transmits the same signal by using the spatialdiversity through three transmitting antennas and different signals aresent by the spatial multiplexing through residual transmitting antennas.

Next, when N_(R) receiving antennas are provided, received signals y₁,y₂, . . . , y_(NR) of the respective antennas are expressed as a vectory as described below.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

Meanwhile, in the case of modeling the channel in the MIMO antennacommunication system, respective channels may be distinguished accordingto transmitting and receiving antenna indexes and a channel passingthrough a receiving antenna i from a transmitting antenna j will berepresented as h_(ij). Herein, it is noted that in the case of the orderof the index of h_(ij), the receiving antenna index is earlier and thetransmitting antenna index is later.

The multiple channels are gathered into one to be expressed even asvector and matrix forms. An example of expression of the vector will bedescribed below.

FIG. 14 is a diagram illustrating a channel from multiple transmittingantennas to one receiving antenna.

As illustrated in FIG. 14, a channel which reaches receiving antenna Ifrom a total of N_(T) transmitting antennas may be expressed as below.h _(i) ^(T) =└h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ┘  [Equation 7]

Further, all of channels passing through N_(R) receiving antennas fromN_(T) transmitting antennas may be shown as below through matrixexpression shown in Equation given above.

$\begin{matrix}{H = {\lbrack \begin{matrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{matrix} \rbrack = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Meanwhile, since additive white Gaussian noise (AWGN) is added afterpassing through a channel matrix H given above in an actual channel,white noises n₁, n₂, . . . , n_(NR) added to N_(R) receiving antennas,respectively are expressed as below.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

Each of the transmission signal, the reception signal, the channel, andthe white noise in the MIMO antenna communication system may beexpressed through a relationship given below by modeling thetransmission signal, the reception signal, the channel, and the whitenoise.

$\begin{matrix}{y = {\lbrack \begin{matrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{matrix} \rbrack = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{matrix} \rbrack} + \lbrack \begin{matrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{matrix} \rbrack} = {{Hx} + n}}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

The numbers of rows and columns of the channel matrix H representing thestate of the channel are determined by the numbers of transmitting andreceiving antennas. In the case of the channel matrix H, the number ofrows becomes equivalent to N_(R) which is the number of receivingantennas and the number of columns becomes equivalent to N_(R) which isthe number of transmitting antennas. That is, the channel matrix Hbecomes an N_(R)×N_(R) matrix.

In general, a rank of the matrix is defined as the minimum number amongthe numbers of independent rows or columns. Therefore, the rank of thematrix may not be larger than the number of rows or columns. As anequation type example, the rank (rank(H)) of the channel matrix H islimited as below.rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

Further, when the matrix is subjected to Eigen value decomposition, therank may be defined as not 0 but the number of Eigen values among theEigen values. By a similar method, when the rank is subjected tosingular value decomposition, the rank may be defined as not 0 but thenumber of singular values. Accordingly, a physical meaning of the rankin the channel matrix may be the maximum number which may send differentinformation in a given channel.

In the present specification, a ‘rank’ for MIMO transmission representsthe number of paths to independently transmit the signal at a specifictime and in a specific frequency resource and ‘the number of layers’represents the number of signal streams transmitted through each path.In general, since the transmitter side transmits layers of the numbercorresponding to the number of ranks used for transmitting the signal,the rank has the same meaning as the number layers if not particularlymentioned.

Reference Signal (RS)

In the wireless communication system, since the data is transmittedthrough the radio channel, the signal may be distorted duringtransmission. In order for the receiver side to accurately receive thedistorted signal, the distortion of the received signal needs to becorrected by using channel information. In order to detect the channelinformation, a signal transmitting method know by both the transmitterside and the receiver side and a method for detecting the channelinformation by using an distortion degree when the signal is transmittedthrough the channel are primarily used. The aforementioned signal isreferred to as a pilot signal or a reference signal (RS).

When the data is transmitted and received by using the MIMO antenna, achannel state between the transmitting antenna and the receiving antennaneed to be detected in order to accurately receive the signal.Therefore, the respective transmitting antennas need to have individualreference signals.

The downlink reference signal includes a common RS (CRS) shared by allterminals in one cell and a dedicated RS (DRS) for a specific terminal.Information for demodulation and channel measurement may be provided byusing the reference signals.

The receiver side (that is, terminal) measures the channel state fromthe CRS and feeds back the indicators associated with the channelquality, such as the channel quality indicator (CQI), the precodingmatrix index (PMI), and/or the rank indicator (RI) to the transmittingside (that is, base station). The CRS is also referred to as acell-specific RS. On the contrary, a reference signal associated with afeed-back of channel state information (CSI) may be defined as CSI-RS.

The DRS may be transmitted through resource elements when datademodulation on the PDSCH is required. The terminal may receive whetherthe DRS is present through the upper layer and is valid only when thecorresponding PDSCH is mapped. The DRS may be referred to as theUE-specific RS or the demodulation RS (DMRS).

FIG. 15 illustrates a reference signal pattern mapped to a downlinkresource block pair in the wireless communication system to which thepresent invention can be applied.

Referring to FIG. 15, as a wise in which the reference signal is mapped,the downlink resource block pair may be expressed by one subframe in thetimedomain×12 subcarriers in the frequency domain. That is, one resourceblock pair has a length of 14 OFDM symbols in the case of a normalcyclic prefix (CP) (FIG. 15a ) and a length of 12 OFDM symbols in thecase of an extended cyclic prefix (CP) (FIG. 15b ). Resource elements(REs) represented as ‘0’, ‘1’, ‘2’, and ‘3’ in a resource block latticemean the positions of the CRSs of antenna port indexes ‘0’, ‘1’, ‘2’,and ‘3’, respectively and resource elements represented as ‘D’ means theposition of the DRS.

Hereinafter, when the CRS is described in more detail, the CRS is usedto estimate a channel of a physical antenna and distributed in a wholefrequency band as the reference signal which may be commonly received byall terminals positioned in the cell. Further, the CRS may be used todemodulate the channel quality information (CSI) and data.

The CRS is defined as various formats according to an antenna array atthe transmitter side (base station). The 3GPP LTE system (for example,release-8) supports various antenna arrays and a downlink signaltransmitting side has three types of antenna arrays of three singletransmitting antennas, two transmitting antennas, and four transmittingantennas. When the base station uses the single transmitting antenna, areference signal for a single antenna port is arrayed. When the basestation uses two transmitting antennas, reference signals for twotransmitting antenna ports are arrayed by using a time divisionmultiplexing (TDM) scheme and/or a frequency division multiplexing (FDM)scheme. That is, different time resources and/or different frequencyresources are allocated to the reference signals for two antenna portswhich are distinguished from each other.

Moreover, when the base station uses four transmitting antennas,reference signals for four transmitting antenna ports are arrayed byusing the TDM and/or FDM scheme. Channel information measured by adownlink signal receiving side (terminal) may be used to demodulate datatransmitted by using a transmission scheme such as single transmittingantenna transmission, transmission diversity, closed-loop spatialmultiplexing, open-loop spatial multiplexing, or multi-user MIMO.

In the case where the MIMO antenna is supported, when the referencesignal is transmitted from a specific antenna port, the reference signalis transmitted to the positions of specific resource elements accordingto a pattern of the reference signal and not transmitted to thepositions of the specific resource elements for another antenna port.That is, reference signals among different antennas are not duplicatedwith each other.

A rule of mapping the CRS to the resource block is defined as below.

$\begin{matrix}{{k = {{6m} + {( {v + v_{shift}} ){mod}\mspace{14mu} 6}}}l = \{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \{ {0,1} \}} \\1 & {{{if}\mspace{14mu} p} \in \{ {2,3} \}}\end{matrix}m} = 0},1,\ldots\mspace{14mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3( {n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} )} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3( {n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} )}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}\mspace{14mu}{mod}\mspace{14mu} 6}} }}} } & \lbrack {{Equation}\mspace{14mu} 12} \rbrack\end{matrix}$

In Equation 12, k and l represent the subcarrier index and the symbolindex, respectively and p represents the antenna port. N_(symb) ^(DL)represents the number of OFDM symbols in one downlink slot and N_(RB)^(DL) represents the number of radio resources allocated to thedownlink. n_(s) represents a slot index and, N_(ID) ^(cell) represents acell ID. mod represents an modulo operation. The position of thereference signal varies depending on the ν_(shift) value in thefrequency domain. Since ν_(shift) is subordinated to the cell ID, theposition of the reference signal has various frequency shift valuesaccording to the cell.

In more detail, the position of the CRS may be shifted in the frequencydomain according to the cell in order to improve channel estimationperformance through the CRS. For example, when the reference signal ispositioned at an interval of three subcarriers, reference signals in onecell are allocated to a 3k-th subcarrier and a reference signal inanother cell is allocated to a 3k+1-th subcarrier. In terms of oneantenna port, the reference signals are arrayed at an interval of sixresource elements in the frequency domain and separated from a referencesignal allocated to another antenna port at an interval of threeresource elements.

In the time domain, the reference signals are arrayed at a constantinterval from symbol index 0 of each slot. The time interval is defineddifferently according to a cyclic shift length. In the case of thenormal cyclic shift, the reference signal is positioned at symbolindexes 0 and 4 of the slot and in the case of the extended CP, thereference signal is positioned at symbol indexes 0 and 3 of the slot. Areference signal for an antenna port having a maximum value between twoantenna ports is defined in one OFDM symbol. Therefore, in the case oftransmission of four transmitting antennas, reference signals forreference signal antenna ports 0 and 1 are positioned at symbol indexes0 and 4 (symbol indexes 0 and 3 in the case of the extended CP) andreference signals for antenna ports 2 and 3 are positioned at symbolindex 1 of the slot. The positions of the reference signals for antennaports 2 and 3 in the frequency domain are exchanged with each other in asecond slot.

Hereinafter, when the DRS is described in more detail, the DRS is usedfor demodulating data. A precoding weight used for a specific terminalin the MIMO antenna transmission is used without a change in order toestimate a channel associated with and corresponding to a transmissionchannel transmitted in each transmitting antenna when the terminalreceives the reference signal.

The 3GPP LTE system (for example, release-8) supports a maximum of fourtransmitting antennas and a DRS for rank 1 beamforming is defined. TheDRS for the rank 1 beamforming also means a reference signal for antennaport index 5.

A rule of mapping the DRS to the resource block is defined as below.Equation 13 shows the case of the normal CP and Equation 14 shows thecase of the extended CP.

$\begin{matrix}{{k = {{( k^{\prime} )\mspace{14mu}{mod}\mspace{14mu} N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \{ {{\begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \{ {2,3} \}} \\{{4m^{\prime}} + {( {2 + v_{shift}} )\mspace{14mu}{mod}\mspace{14mu} 4}} & {{{if}\mspace{14mu} l} \in \{ {5,6} \}}\end{matrix}l} = \{ {{\begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix}l^{\prime}} = \{ {{{\begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{3\; N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}\mspace{14mu}{mod}\mspace{14mu} 3}}} } } }} & \lbrack {{Equation}\mspace{14mu} 13} \rbrack \\{{k = {{( k^{\prime} )\mspace{14mu}{mod}\mspace{14mu} N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \{ {{\begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {( {2 + v_{shift}} )\mspace{14mu}{mod}\mspace{14mu} 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix}l} = \{ {{\begin{matrix}4 & {l^{\prime} \in \{ {0,2} \}} \\1 & {l^{\prime} = 1}\end{matrix}l^{\prime}} = \{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{4\; N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}\mspace{14mu}{mod}\mspace{14mu} 3}}} } } }} & \lbrack {{Equation}\mspace{14mu} 14} \rbrack\end{matrix}$

In Equations 12 to 14 given above, k and p represent the subcarrierindex and the antenna port, respectively. N_(RB) ^(DL), n_(s), andN_(ID) ^(cell) represent the number of RBs, the number of slot indexes,and the number of cell IDs allocated to the downlink, respectively. Theposition of the RS varies depending on the ν_(shift) value in terms ofthe frequency domain.

In Equations 13 and 14, k and l represent the subcarrier index and thesymbol index, respectively and p represents the antenna port. N_(sc)^(RB) represents the size of the resource block in the frequency domainand is expressed as the number of subcarriers. n_(PRB) represents thenumber of physical resource blocks. N_(RB) ^(PDSCH) represents afrequency band of the resource block for the PDSCH transmission. n_(s)represents the slot index and N_(ID) ^(cell) represents the cell ID. modrepresents the modulo operation. The position of the reference signalvaries depending on the ν_(shift) value in the frequency domain. Sinceν_(shift) is subordinated to the cell ID, the position of the referencesignal has various frequency shift values according to the cell.

Sounding Reference Signal (SRS)

The SRS is primarily used for the channel quality measurement in orderto perform frequency-selective scheduling and is not associated withtransmission of the uplink data and/or control information. However, theSRS is not limited thereto and the SRS may be used for various otherpurposes for supporting improvement of power control and variousstart-up functions of terminals which have not been scheduled. Oneexample of the start-up function may include an initial modulation andcoding scheme (MCS), initial power control for data transmission, timingadvance, and frequency semi-selective scheduling. In this case, thefrequency semi-selective scheduling means scheduling that selectivelyallocates the frequency resource to the first slot of the subframe andallocates the frequency resource by pseudo-randomly hopping to anotherfrequency in the second slot.

Further, the SRS may be used for measuring the downlink channel qualityon the assumption that the radio channels between the uplink and thedownlink are reciprocal. The assumption is valid particularly in thetime division duplex in which the uplink and the downlink share the samefrequency spectrum and are divided in the time domain.

Subframes of the SRS transmitted by any terminal in the cell may beexpressed by a cell-specific broadcasting signal. A 4-bit cell-specific‘srsSubframeConfiguration’ parameter represents 15 available subframearrays in which the SRS may be transmitted through each radio frame. Bythe arrays, flexibility for adjustment of the SRS overhead is providedaccording to a deployment scenario.

A 16-th array among them completely turns off a switch of the SRS in thecell and is suitable primarily for a serving cell that serves high-speedterminals.

FIG. 16 illustrates an uplink subframe including a sounding referencesignal symbol in the wireless communication system to which the presentinvention can be applied.

Referring to FIG. 16, the SRS is continuously transmitted through a lastSC FDMA symbol on the arrayed subframes. Therefore, the SRS and the DMRSare positioned at different SC-FDMA symbols.

The PUSCH data transmission is not permitted in a specific SC-FDMAsymbol for the SRS transmission and consequently, when sounding overheadis highest, that is, even when the SRS symbol is included in allsubframes, the sounding overhead does not exceed approximately 7%.

Each SRS symbol is generated by a base sequence (random sequence or asequence set based on Zadoff-Ch (ZC)) associated with a given time wiseand a given frequency band and all terminals in the same cell use thesame base sequence. In this case, SRS transmissions from a plurality ofterminals in the same cell in the same frequency band and at the sametime are orthogonal to each other by different cyclic shifts of the basesequence to be distinguished from each other.

SRS sequences from different cells may be distinguished from each otherby allocating different base sequences to respective cells, butorthogonality among different base sequences is not assured.

Coordinated Multi-Point Transmission and Reception (COMP)

According to a demand of LIE-advanced, CoMP transmission is proposed inorder to improve the performance of the system. The CoMP is also calledco-MIMO, collaborative MIMO, network MIMO, and the like. It isanticipated that the CoMP will improves the performance of the terminalpositioned at a cell edge and improve an average throughput of the cell(sector).

In general, inter-cell interference decreases the performance and theaverage cell (sector) efficiency of the terminal positioned at the celledge in a multi-cell environment in which a frequency reuse index is 1.In order to alleviate the inter-cell interference, the LTE system adoptsa simple passive method such as fractional frequency reuse (FFR) in theLTE system so that the terminal positioned at the cell edge hasappropriate performance efficiency in an interference-limitedenvironment. However, a method that reuses the inter-cell interferenceor alleviates the inter-cell interference as a signal (desired signal)which the terminal needs to receive is more preferable instead ofreduction of the use of the frequency resource for each cell. The CoMPtransmission scheme may be adopted in order to achieve theaforementioned object.

The CoMP scheme which may be applied to the downlink may be classifiedinto a joint processing (JP) scheme and a coordinatedscheduling/beamforming (CS/CB) scheme.

In the JP scheme, the data may be used at each point (base station) in aCoMP wise. The CoMP wise means a set of base stations used in the CoMPscheme. The JP scheme may be again classified into a joint transmissionscheme and a dynamic cell selection scheme.

The joint transmission scheme means a scheme in which the signal issimultaneously transmitted through a plurality of points which are allor fractional points in the CoMP wise. That is, data transmitted to asingle terminal may be simultaneously transmitted from a plurality oftransmission points. Through the joint transmission scheme, the qualityof the signal transmitted to the terminal may be improved regardless ofcoherently or non-coherently and interference with another terminal maybe actively removed.

The dynamic cell selection scheme means a scheme in which the signal istransmitted from the single point through the PDSCH in the CoMP wise.That is, data transmitted to the single terminal at a specific time istransmitted from the single point and data is not transmitted to theterminal at another point in the CoMP wise. The point that transmits thedata to the terminal may be dynamically selected.

According to the CS/CB scheme, the CoMP wise performs beamformingthrough coordination for transmitting the data to the single terminal.That is, the data is transmitted to the terminal only in the servingcell, but user scheduling/beamforming may be determined throughcoordination of a plurality of cells in the CoMP wise.

In the case of the uplink, CoMP reception means receiving the signaltransmitted by the coordination among a plurality of points which aregeographically separated. The CoMP scheme which may be applied to theuplink may be classified into a joint reception (JR) scheme and thecoordinated scheduling/beamforming (CS/CB) scheme.

The JR scheme means a scheme in which the plurality of points which areall or fractional points receives the signal transmitted through thePDSCH in the CoMP wise. In the CS/CB scheme, only the single pointreceives the signal transmitted through the PDSCH, but the userscheduling/beamforming may be determined through the coordination of theplurality of cells in the CoMP wise.

Relay Node (RN)

The relay node transfers data transmitted and received between the basestation and the terminal through two different links (a backhaul linkand an access link). The base station may include a donor cell. Therelay node is wirelessly connected to a wireless access network throughthe donor cell.

Meanwhile, in respect to the use of a band (spectrum) of the relay node,a case in which the backhaul link operates in the same frequency band asthe access link is referred to as ‘in-band’ and a case in which thebackhaul link and the access link operate in different frequency bandsis referred to as ‘out-band’. In both the cases of the in-band and theout-band, a terminal (hereinafter, referred to as a legacy terminal)that operates according to the existing LTE system (for example,release-8) needs to be able to access the donor cell.

The relay node may be classified into a transparent relay node or anon-transparent relay node according to whether the terminal recognizingthe relay node. Transparent means a case in which it may not berecognized whether the terminal communicates with the network throughthe relay node and non-transparent means a case in which it isrecognized whether the terminal communicates with the network throughthe relay node.

In respect to control of the relay node, the relay node may be dividedinto a relay node which is constituted as a part of the donor cell or arelay node that autonomously controls the cell.

The relay node which is constituted as a part of the donor cell may havea relay node identity (ID), but does not have a cell identity thereof.

When at least a part of radio resource management (RRM) is controlled bya base station to which the donor cell belongs, even though residualparts of the RRM are positioned at the relay node, the relay node isreferred to as the relay node which is constituted as a part of thedonor cell. Preferably, the relay node may support the legacy terminal.For example, various types including smart repeaters, decode-and-forwardrelay nodes, L2 (second layer) relay nodes, and the like and a type-2relay node correspond to the relay node.

In the case of the relay node that autonomously controls the cell, therelay node controls one or a plurality of cells and unique physicallayer cell identities are provided to the respective cells controlled bythe relay node. Further, the respective cells controlled by the relaynode may use the same RRM mechanism. In terms of the terminal, there isno difference between accessing the cell controlled by the relay nodeand accessing a cell controlled by a general base station. The cellcontrolled by the relay node may support the legacy terminal. Forexample, a self-backhauling relay node, an L3 (third layer) relay node,a type-1 relay node, and a type-1a relay node correspond to the relaynode.

The type-1 relay node as the in-band relay node controls a plurality ofcells and the plurality of respective cells are recognized as separatecells distinguished from the donor cell in terms of the terminal.Further, the plurality of respective cells may have physical cell IDs(they are defined in the LTE release-8) and the relay node may transmita synchronization channel, the reference signal, and the like thereof.In the case of a single-cell operation, the terminal may receivescheduling information and an HARQ feedback directly from the relay nodeand transmit control channels (scheduling request (SR), CQI, ACK/NACK,and the like) thereof to the relay node. Further, the type-1 relay nodeis shown as a legacy base station (a base station that operatesaccording to the LTE release-8 system) to the legacy terminals (terminalthat operate according to the LTE release-8 system). That is, the type-1relay node has the backward compatibility. Meanwhile, the terminals thatoperate according to the LTE-A system recognize the type-1 relay node asa base station different from the legacy base station to provideperformance improvement.

The type-1a relay node has the same features as the type-1 relay nodeincluding operating as the out-band The operation of the type-1a relaynode may be configured so that an influence on an L1 (first layer)operation is minimized or is not present.

The type-2 relay node as the in-band relay node does not have a separatephysical cell ID, and as a result, a new cell is not formed. The type-2relay node is transparent with respect to the legacy terminal and thelegacy terminal may not recognize the presence of the type-2 relay node.The type-2 relay node may transmit the PDSCH, but at least does nottransmit the CRS and the PDCCH.

Meanwhile, in order for the relay node to operate as the in-band, someresources in the time-frequency space needs to be reserved for thebackhaul link and the resources may be configured not to be used for theaccess link. This is referred to as resource partitioning.

A general principle in the resource partitioning in the relay node maybe described as below. Backhaul downlink and access downlink may bemultiplexed in the time division multiplexing scheme on one carrierfrequency (that is, only one of the backhaul downlink and the accessdownlink is activated at a specific time). Similarly, backhaul uplinkand access uplink may be multiplexed in the time division multiplexingscheme on one carrier frequency (that is, only one of the backhauluplink and the access uplink is activated at a specific time).

In the backhaul link multiplexing in the FDD, backhaul downlinktransmission may be performed in a downlink frequency band and backhauluplink transmission may be performed in an uplink frequency band. In thebackhaul link multiplexing in the TDD, THE backhaul downlinktransmission may be performed in the downlink subframe of the basestation and the relay node and the backhaul uplink transmission may beperformed in the uplink subframe of the base station and the relay node.

In the case of the in-band relay node, for example, when both backhauldownlink reception from the base station and access downlinktransmission to the terminal are performed in the same frequency band,signal interference may occurs at a receiver side of the relay node by asignal transmitted from a transmitter side of the relay node. That is,the signal interference or RF jamming may occur at an RF front-end ofthe relay node. Similarly, even when both the backhaul uplinktransmission to the base station and the access uplink reception fromthe terminal are performed in the same frequency band, the signalinterference may occur.

Therefore, in order for the relay node to simultaneously transmit andreceive the signal in the same frequency band, when sufficientseparation (for example, the transmitting antenna and the receivingantenna are installed to be significantly geographically spaced apartfrom each other like installation on the ground and underground) betweena received signal and a transmitted signal is not provided, it isdifficult to implement the transmission and reception of the signal.

As one scheme for solving a problem of the signal interference, therelay node operates not transmit the signal to the terminal whilereceiving the signal from the donor cell. That is, a gap is generated intransmission from the relay node to the terminal and the terminal may beconfigured not to expect any transmission from the relay node during thegap. The gap may be configured to constitute a multicast broadcastsingle frequency network (MBSFN) subframe.

FIG. 17 illustrates a structure of relay resource partitioning in thewireless communication system to which the present invention can beapplied.

In FIG. 17, in the case of a first subframe as a general subframe, adownlink (that is, access downlink) control signal and downlink data aretransmitted from the relay node and in the case of a second subframe asthe MBSFN subframe, the control signal is transmitted from the relaynode from the terminal in the control region of the downlink subframe,but no transmission is performed from the relay node to the terminal inresidual regions. Herein, since the legacy terminal expects transmissionof the PDCCH in all downlink subframes (in other words, since the relaynode needs to support legacy terminals in a region thereof to perform ameasurement function by receiving the PDCCH every subframe), the PDCCHneeds to be transmitted in all downlink subframes for a correctoperation of the legacy terminal. Therefore, eve on a subframe (secondsubframe) configured for downlink (that is, backhaul downlink)transmission from the base station to the relay node, the relay does notreceive the backhaul downlink but needs to perform the access downlinktransmission in first N (N=1, 2, or 3) OFDM symbol intervals of thesubframe. In this regard, since the PDCCH is transmitted from the relaynode to the terminal in the control region of the second subframe, thebackward compatibility to the legacy terminal, which is served by therelay node may be provided. In residual regions of the second subframe,the relay node may receive transmission from the base station while notransmission is performed from the relay node to the terminal.Therefore, through the resource partitioning scheme, the access downlinktransmission and the backhaul downlink reception may not besimultaneously performed in the in-band relay node.

The second subframe using the MBSFN subframe will be described indetail. The control region of the second subframe may be referred to asa relay non-hearing interval. The relay non-hearing interval means aninterval in which the relay node does not receive the backhaul downlinksignal and transmits the access downlink signal. The interval may beconfigured by the OFDM length of 1, 2, or 3 as described above. In therelay node non-hearing interval, the relay node may perform the accessdownlink transmission to the terminal and in the residual regions, therelay node may receive the backhaul downlink from the base station. Inthis case, since the relay node may not simultaneously performtransmission and reception in the same frequency band, It takes a timefor the relay node to switch from a transmission mode to a receptionmode. Therefore, in a first partial interval of a backhaul downlinkreceiving region, a guard time (GT) needs to be set so that the relaynode switches to the transmission/reception mode. Similarly, even whenthe relay node operates to receive the backhaul downlink from the basestation and transmit the access downlink to the terminal, the guard timefor the reception/transmission mode switching of the relay node may beset. The length of the guard time may be given as a value of the timedomain and for example, given as a value of k (k≥1) time samples (Ts) orset to the length of one or more OFDM symbols. Alternatively, when therelay node backhaul downlink subframes are consecutively configured oraccording to a predetermines subframe timing alignment relationship, aguard time of a last part of the subframe may not be defined or set. Theguard time may be defined only in the frequency domain configured forthe backhaul downlink subframe transmission in order to maintain thebackward compatibility (when the guard time is set in the accessdownlink interval, the legacy terminal may not be supported). In thebackhaul downlink reception interval other than the guard time, therelay node may receive the PDCCH and the PDSCH from the base station.This may be expressed as a relay (R)-PDCCH and a relay-PDSCH (R-PDSCH)in a meaning of a relay node dedicated physical channel.

Channel State Information (CSI) Feed-Back

The MIMO scheme may be divided into an open-loop scheme and aclosed-loop scheme. The open-loop MIMO scheme means that the transmitterside performs MIMO transmission without a feed-back of the channel stateinformation from the MIMO receiver side. The closed-loop MIMO schememeans that the transmitter side performs the MIMO transmission byreceiving the feed-back of the channel state information from the MIMOreceiver side. In the closed-loop MIMO scheme, each of the transmitterside and the receiver side may perform the beamforming based on thechannel state information in order to acquire a multiplexing gain of theMIMO transmitting antenna. The transmitter side (for example, the basestation) may allocate an uplink control channel or an uplink sharechannel to the receiver side (for example, the terminal).

The channel state information (CSI) which is fed back may include therank indicator (RI), the precoding matrix index (PMI), and the channelquality indicator (CQI).

The RI is information on the rank of the channel. The rank of thechannel means the maximum number of layers (alternatively, streams)which may send different information through the same time-frequencyresource. Since a rank value is primary determined by long-time fadingof the channel, the RI may be generally fed back according to a longerperiod (that is, less frequently) than the PMI and the CQI.

The PMI is information on the precoding matrix used for transmissionfrom the transmitter side and a value acquired by reflecting spatialcharacteristics of the channel. Precoding means mapping the transmissionlayer to the transmitting antenna and a layer-antenna mappingrelationship may be determined by a precoding matrix. The PMIcorresponds to a precoding matrix index of the base station, which theterminal prefers to based on a measurement value (metric) such as asignal-to-interference plus noise ratio (SINR), or the like. In order toreduce feed-back overhead of precoding information, a scheme may beused, in which the transmitter side and the receiver side previouslyshare a codebook including various precoding matrices and feed back onlyan index indicating a specific precoding matrix.

The CQI is information indicating the channel quality or a channelintensity. The CQI may be expressed as a predetermined MCS combination.That is, the CQI which is fed back indicates a corresponding modulationscheme and a corresponding code rate. In general, the CQI becomes avalue acquired by reflecting a received SINR which may be acquired whenthe base station configures a spatial channel by using the PMI.

In the system (for example, LTE-A system) supporting the extendedantenna configuration, acquiring additional multi-user diversity byusing a multi-user-MIMO (MU-MIMO) scheme is considered. In the MU-MIMOscheme, since an interference channel between terminals multiplexed inan antenna domain is present, when the base station performs downlinktransmission by using the channel state information which one terminalamong the multi users feeds back, the interference in another terminalneeds to be prevented. Therefore, channel state information havinghigher accuracy needs to be fed back than a single-user-MIMO (SU-MIMO)scheme in order to correctly perform the MU-MIMO operation.

A new CSI feed-back scheme that enhances the CSI constituted by the RI,the PMI, and the CQI may be adopted in order to measure and report themore accurate channel state information. For example, the precodinginformation which the receiver side feeds back may be indicated bycombining two PMIs. One (first PMI) among two PMIs may have an attributeof a long term and/or a wideband and be designated as W1. The other one(second PMI) among two PMIs may have an attribute of a short term and/ora subband and be designated as W2. A final PMI may be determined by acombination (alternatively, function) of W1 and W2. For example, whenthe final PMI is referred to as W, W may be defined as W=W1*W2 orW=W2*W1.

Herein, W1 reflects average frequency and/or temporal characteristics ofthe channel. In other words, W may be defined as the channel stateinformation reflecting a characteristic of a long term channel on thetime, reflecting a characteristic of a wideband channel on thefrequency, or reflecting the characteristics of the long term channel onthe time and the wideband channel on the frequency. In order to expressthe characteristics of W1 in brief, W1 is referred to as the channelstate information (alternatively, long term-wideband PMI) of the longterm and wideband attributes.

Meanwhile, W2 reflects a relatively more instantaneous channelcharacteristic than W1. In other words, W2 may be defined as the channelstate information reflecting a characteristic of a short-term channel onthe time, reflecting a characteristic of a subband channel on thefrequency, or reflecting the characteristics of the short term channelon the time and the subband channel on the frequency. In order toexpress the characteristics of W2 in brief, W2 is referred to as thechannel state information (alternatively, short term-subband PMI) of theshort term and subband attributes.

In order to determine one final precoding matrix W from the information(for example, W1 and W2) of two different attributes indicating thechannel state, separate codebooks (that is, a first codebook for W1 anda second codebook for W2) constituted by the precoding matrixesindicating the channel information of the respective attributes need tobe configured. A type of the codebook configured as above may bereferred to as a hierarchical codebook. Further, determining a codebookto be finally used by using the hierarchical codebook may be referred toas hierarchical codebook transformation.

In the case of using the code book, higher-accuracy channel feed-back ispossible than in the case of using a single codebook. Single-cellMU-MIMO and/or multi-cell coordinated communication may be supported byusing the high-accuracy channel feed-back.

Enhanced PMI for MU-MIMO or CoMP

In a next-generation communication standard such as LTE-A, in order toachieve high transmission rate, transmission schemes such as MU-MIMO andCoMP were proposed. In order to implement the improved transmissionschemes, the UE needs to feedback complicated and various CSIs to thebase station.

For example, in the MU-MIMO, when UE-A selects the PMI, a CSI feedbackscheme which uploads desired PMI of the UE-A and the PMI (hereinafter,referred to as best companion PMI (BCPMI)) of the UE scheduled with theUE-A.

That is, in the precoding matrix codebook, when co-scheduled UE is usedas a precoder, the BCPMI which gives less interference to the UE-A iscalculated and additionally fed-back to the base station.

The base station MU-MIMO-schedules another UE preferring UE-A and bestcompanion precoding matrix (BCPM) (precoding matrix corresponding to theBCPMI) precoding by using the information.

The BCPMI feedback scheme is divided into two of an explicit feedbackand an implicit feedback according to presence and absence of thefeedback payload.

First, there is the explicit feedback scheme with the feedback payload.

In the explicit feedback scheme, the UE-A determines the BCPMI in theprecoding matrix codebook and then feedbacks the determined BCPMI to thebase station through a control channel. As one scheme, the UE-A selectsan interference signal precoding matrix in which estimated SINR ismaximized in the codebook and feedbacks the selected interference signalprecoding matrix as the BCPMI value.

As an advantage of the explicit feedback, the BCPMI with more effectiveinterference removal may be selected and transmitted. The UE determinesthe most effective value in the interference removal as the BCPMI byassuming all the codewords in the codebook one by one as theinterference beam and comparing the metric such as SINR. However, as thecodebook size is increased, the candidates of the BCPMI are increased,and thus the larger feedback payload size is required.

Second, there is the explicit feedback scheme without the feedbackpayload.

The implicit feedback scheme is a scheme that the UE-A does not search acodeword which receives less interference in the codebook to select thesearched codeword as the BCPMI, but statically determines the BCPMIcorresponding to the desired PMI when the desired PMI is determined. Inthis case, it may be preferred that the BCPM is constituted byorthogonal vectors in the determined desired PMI.

The reason is that the desired PM is set in a direction to maximize thechannel gain of the channel H in order to maximize the received SINR andthus, it is effective in mitigating the interference the interferencesignal is selected by avoiding in the direction of the PM. When thechannel H is analyzed as the plurality of independent channels throughthe singular value decomposition (SVD), the BCPMI determination schemeis further justified. 4×4 channel H may be decomposed through the SVDlike the following Equation 15.

$\begin{matrix}{H = {{ULV}^{H} = \lbrack \begin{matrix}u_{1} & u_{2} & u_{3} & {{ u_{4} \rbrack\begin{bmatrix}\lambda_{1} & 0 & 0 & 0 \\0 & \lambda_{2} & 0 & 0 \\0 & 0 & \lambda_{3} & 0 \\0 & 0 & 0 & \lambda_{4}\end{bmatrix}}\begin{bmatrix}v_{1}^{H} \\v_{2}^{H} \\v_{3}^{H} \\v_{4}^{H}\end{bmatrix}}\end{matrix} }} & \lbrack {{Equation}\mspace{14mu} 15} \rbrack\end{matrix}$

In Equation 15, U,V are unitary matrices, u_(i), v_(i), and λ_(i)represent a 4×1 left singular vector, a 4×1 right singular vector, and asingular value of the channel H, respectively and arranged in descendingorder of λ_(i)>λ_(i+1). In the case of using the beamforming matrix V inthe transmission terminal and the beamforming matrix U^(H) in thereception terminal, all channel gains which may be theoreticallyobtained may be obtained without loss.

In the case of Rank 1, using the transmission beamforming vector v₁ andthe reception beamforming vector u1 may obtain the channel |λ_(i)|² togain obtain optimal performance in terms of the SNR. For example, it isadvantageous that the UE-A selects the most similar PM to v₁ in the caseof rank 1. Ideally, when the desired PM completely coincides with v₁,the reception beam is set to u₁ and the transmission beam of theinterference signal is set to the PM in the orthogonal direction tocompletely remove the interference signal without loss in the desiredsignal. Actually, due to the quantization error, when the desired PM hasa slight difference from v₁, the transmission beam of the interferencesignal set in the orthogonal direction to the PM is no longer equal tothe orthogonal beam to v₁, and thus, the desired signal may notcompletely remove the interference signal without loss of the desiredsignal, but when the quantization error is small to help in controllingthe interference signal.

As an example of the implicit feedback, in the case of using the LTEcodebook, the BCPMI may be statically determined as the vector indexorthogonal to the PMI.

It is assumed that the transmission antennas are four and the receptionrank of the UE feedbacking the PMI is 1, three vectors orthogonal to thedesired PMI are expressed as three BCPMIs.

For example, in the case of PMI=3, BCPMI=0, 1, 2. The PMI and the BCPMIrepresent the index of the 4×1 vector codeword in the codebook. The basestation uses some or all as the precoder of the co-schedule UE byconsidering the BCPMI set (BCPMI=0, 1, 2) as the effective precodingindex in the interference removal.

The implicit PMI has an advantage in that there is no additionalfeedback overhead because the desired PMI and the BCPMI set are mappedto 1:1. However, due to the quantization error of the desired PM (PM:precoding matrix corresponding to the PMI), the BCPM subordinatedthereto may have optimal beam direction and error for the interferenceremoval. When there is no quantization error, three BCPMs representinterference beam (ideal interference beam) which completely removes allthe interference, but when there is the error, each BCPM occurs adifference from the ideal interference beam.

Further, the difference from the ideal interference beam of each BCPM isaveragely the same, but may be different at a certain moment. Forexample, when desired PMI=3, it may be effective in removing theinterference signal in order of BCPMI 0, 1, and 2, and the base stationwhich does not know a relative error of BCPMI 0, 1, and 2 maycommunicate while the strong interference between the co-scheduled UEsis present by determining BCPMI 2 with the largest error with the idealinterference beam as the beam of the interference signal.

General D2D Communication

Generally, D2D communication is limitatively used as the term forcommunication between objects or object intelligent communication, butthe D2D communication in the present invention may include allcommunication between various types of devices having a communicationfunction such as a smart phone and a personal computer in addition tosimple devices with a communication function.

FIG. 18 is a diagram for schematically describing the D2D communicationin a wireless communication system to which the present invention may beapplied.

FIG. 18A illustrates a communication scheme based on an existing basestation eNB, and the UE1 may transmit the data to the base station onthe uplink and the base station may transmit the data to the UE2 on thedownlink. The communication scheme may be referred to as an indirectcommunication scheme through the base station. In the indirectcommunication scheme, a Un link (referred to as a backhole link as alink between base stations or a link between the base station and therepeater) and/or a Uu link (referred to as an access link as a linkbetween the base station and the UE or a link between the repeater andthe UE) which are defined in the existing wireless communication systemmay be related.

FIG. 18B illustrates a UE-to-UE communication scheme as an example ofthe D2D communication, and the data exchange between the UEs may beperformed without passing through the base station. The communicationscheme may be referred to as a direct communication scheme betweendevices. The D2D direct communication scheme has advantages of reducinglatency and using smaller wireless resources as compared with theexisting indirect communication scheme through the base station.

FIG. 19 illustrates examples of various scenarios of the D2Dcommunication to which the method proposed in the specification may beapplied.

The D2D communication scenario may be divided into (1) anout-of-coverage network, (2) a partial-coverage network, and (3)in-coverage network according to whether the UE1 and the UE2 arepositioned in coverage/out-of-coverage.

The in-coverage network may be divided into an in-coverage-single-celland an in-coverage-multi-cell according to the number of cellscorresponding to the coverage of the base station.

FIG. 19a illustrates an example of an out-of-coverage network scenarioof the D2D communication.

The out-of-coverage network scenario means perform the D2D communicationbetween the D2D UEs without control of the base station.

In FIG. 19a , only the UE1 and the UE2 are present and the UE1 and theUE2 may directly communicate with each other.

FIG. 19b illustrates an example of a partial-coverage network scenarioof the D2D communication.

The partial-coverage network scenario means performing the D2Dcommunication between the D2D UE positioned in the network coverage andthe D2D UE positioned out of the network coverage.

In FIG. 19b , it may be illustrated that the D2D UE positioned in thenetwork coverage and the D2D UE positioned out of the network coveragecommunicate with each other.

FIG. 19c illustrates an example of the in-coverage-single-cell and FIG.19d illustrates an example of the in-coverage-multi-cell scenario.

The in-coverage network scenario means that the D2D UEs perform the D2Dcommunication through the control of the base station in the networkcoverage.

In FIG. 19c , the UE1 and the UE2 are positioned in the same networkcoverage (alternatively, cell) under the control of the base station.

In FIG. 19d , the UE1 and the UE2 are positioned in the networkcoverage, but positioned in different network coverages. In addition,the UE1 and the UE2 performs the D2D communication under the control ofthe base station managing the network coverage.

Here, the D2D communication will be described in more detail.

The D2D communication may operate in the scenario illustrated in FIG.19, but generally operate in the network coverage and out of the networkcoverage. The link used for the D2D communication (direct communicationbetween the UEs) may be referred to as D2D link, directlink, orsidelink, but for the convenience of description, the link is commonlyreferred to as the sidelink.

The sidelink transmission may operate in uplink spectrum in the case ofthe FDD and in the uplink (alternatively, downlink) subframe in the caseof the TDD. For multiplexing the sidelink transmission and the uplinktransmission, time division multiplexing (TDM) may be used.

The sidelink transmission and the uplink transmission do notsimultaneously occur. In the uplink subframe used for the uplinktransmission and the sidelink subframe which partially or entirelyoverlaps with UpPTS, the sidelink transmission does not occur.Alternatively, the transmission and the reception of the sidelink do notsimultaneously occur.

A structure of a physical resource used in the sidelink transmission maybe used equally to the structure of the uplink physical resource.However, the last symbol of the sidelink subframe is constituted by aguard period and not used in the sidelink transmission.

The sidelink subframe may be constituted by extended CP or normal CP.

The D2D communication may be largely divided into discovery, directcommunication, and synchronization.

1) Discovery

The D2D discovery may be applied in the network coverage. (includinginter-cell and intra-cell). Displacement of synchronous or asynchronouscells may be considered in the inter-cell coverage. The D2D discoverymay be used for various commercial purposes such as advertisement,coupon issue, and finding friends to the UE in the near area.

When the UE 1 has a role of the discovery message transmission, the UE 1transmits the discovery message and the UE 2 receives the discoverymessage. The transmission and the reception of the UE 1 and the UE 2 maybe reversed. The transmission from the UE 1 may be received by one ormore UEs such as UE2.

The discovery message may include a single MAC PDU, and here, the singleMAC PDU may include a UE ID and an application ID.

A physical sidelink discovery channel (PSDCH) may be defined as thechannel transmitting the discovery message. The structure of the PSDCHchannel may reuse the PUSCH structure.

A method of allocating resources for the D2D discovery may use two typesType 1 and Type 2.

In Type 1, eNB may allocate resources for transmitting the discoverymessage by a non-UE specific method.

In detail, a wireless resource pool for discovery transmission andreception constituted by the plurality of subframes is allocated at apredetermined period, and the discovery transmission UE transmits thenext discovery message which randomly selects the specific resource inthe wireless resource pool.

The periodical discovery resource pool may be allocated for thediscovery signal transmission by a semi-static method. Settinginformation of the discovery resource pool for the discoverytransmission includes a discovery period, the number of subframes whichmay be used for transmission of the discovery signal in the discoveryperiod (that is, the number of subframes constituted by the wirelessresource pool).

In the case of the in-coverage UE, the discovery resource pool for thediscovery transmission is set by the eNB and may notified to the UE byusing RRC signaling (for example, a system information block (SIB)).

The discovery resource pool allocated for the discovery in one discoveryperiod may be multiplexed to TDM and/or FDM as a time-frequency resourceblock with the same size, and the time-frequency resource block with thesame size may be referred to as a ‘discovery resource’.

The discovery resource may be used for transmitting the discovery MACPDU by one UE. The transmission of the MAC PDU transmitted by one UE maybe repeated (for example, repeated four times) contiguously ornon-contiguously in the discovery period (that is, the wireless resourcepool). The UE randomly selects the first discovery resource in thediscovery resource set) which may be used for the repeated transmissionof the MAC PDU and other discovery resources may be determined inrelation with the first discovery resource. For example, a predeterminedpattern is preset and according to a position of the first selecteddiscovery resource, the next discovery resource may be determinedaccording to a predetermined pattern. Further, the UE may randomlyselect each discovery resource in the discovery resource set which maybe used for the repeated transmission of the MAC PDU.

In Type 2, the resource for the discovery message transmission isUE-specifically allocated. Type 2 is sub-divided into Type-2A andType-2B again. Type-2A is a type in which the UE allocates the resourceevery transmission instance of the discovery message in the discoveryperiod, and the type 2B is a type in which the resource is allocated bya semi-persistent method.

In the case of Type 2B, RRC_CONNECTED UE request allocation of theresource for transmission of the D2D discovery message to the eNBthrough the RRC signaling. In addition, the eNB may allocate theresource through the RRC signaling. When the UE is transited to aRRC_IDLE state or the eNB withdraws the resource allocation through theRRC signaling, the UE releases the transmission resource allocated last.As such, in the case of the type 2B, the wireless resource is allocatedby the RRC signaling and activation/deactivation of the wirelessresource allocated by the PDCCH may be determined.

The wireless resource pool for the discovery message reception is set bythe eNB and may notified to the UE by using RRC signaling (for example,a system information block (SIB)).

The discovery message reception UE monitors all of the discoveryresource pools of Type 1 and Type 2 for the discovery message reception.

2) Direct Communication

An application area of the D2D direct communication includes in-coverageand out-of-coverage, and edge-of-coverage. The D2D direct communicationmay be used on the purpose of public safety (PS) and the like.

When the UE 1 has a role of the direct communication data transmission,the UE 1 transmits direct communication data and the UE 2 receivesdirect communication data. The transmission and the reception of the UE1 and the UE 2 may be reversed. The direct communication transmissionfrom the UE 1 may be received by one or more UEs such as UE2.

The D2D discovery and the D2D communication are not associated with eachother and independently defined. That is, the in groupcast and broadcastdirect communication, the D2D discovery is not required. As such, whenthe D2D discovery and the D2D communication are independently defined,the UEs need to recognize the adjacent UEs. In other words, in the caseof the groupcast and broadcast direct communication, it is not requiredthat all of the reception UEs in the group are close to each other.

A physical sidelink shared channel (PSSCH) may be defined as a channeltransmitting D2D direct communication data. Further, a physical sidelinkcontrol channel (PSCCH) may be defined as a channel transmitting controlinformation (for example, scheduling assignment (SA) for the directcommunication data transmission, a transmission format, and the like)for the D2D direct communication. The PSSCH and the PSCCH may reuse thePUSCH structure.

A method of allocating the resource for D2D direct communication may usetwo modes mode 1 and mode 2.

Mode 1 means a mode of scheduling a resource used for transmitting dataor control information for D2D direct communication. Mode 1 is appliedto in-coverage.

The eNB sets a resource pool required for D2D direct communication.Here, the resource pool required for D2D direct communication may bedivided into a control information pool and a D2D data pool. When theeNB schedules the control information and the D2D data transmissionresource in the pool set to the transmission D2D UE by using the PDCCHor the ePDCCH, the transmission D2D UE transmits the control informationand the D2D data by using the allocated resource.

The transmission UE requests the transmission resource to the eNB, andthe eNB schedules the control information and the resource fortransmission of the D2D direct communication data. That is, in the caseof mode 1, the transmission UE needs to be in an RRC_CONNECTED state inorder to perform the D2D direct communication. The transmission UEtransmits the scheduling request to the eNB and a buffer status report(BSR) procedure is performed so that the eNB may determine an amount ofresource required by the transmission UE.

The reception UEs monitor the control information pool and mayselectively decode the D2D data transmission related with thecorresponding control information when decoding the control informationrelated with the reception UEs. The reception UE may not decode the D2Ddata pool according to the control information decoding result.

Mode 2 means a mode in which the UE arbitrarily selects the specificresource in the resource pool for transmitting the data or the controlinformation for D2D direct communication. In the out-of-coverage and/orthe edge-of-coverage, the mode 2 is applied.

In mode 2, the resource pool for transmission of the control informationand/or the resource pool for transmission of the D2D directcommunication data may be pre-configured or semi-statically set. The UEreceives the set resource pool (time and frequency) and selects theresource for the D2D direct communication transmission from the resourcepool. That is, the UE may select the resource for the controlinformation transmission from the control information resource pool fortransmitting the control information. Further, the UE may select theresource from the data resource pool for the D2D direct communicationdata transmission.

In D2D broadcast communication, the control information is transmittedby the broadcasting UE. The control information explicitly and/orimplicitly indicate the position of the resource for the data receptionin associated with the physical channel (that is, the PSSCH)transporting the D2D direct communication data.

3) Synchronization

A D2D synchronization signal (alternatively, a sidelink synchronizationsignal) may be used so that the UE obtains time-frequencysynchronization. Particularly, in the case of the out-of-coverage, sincethe control of the eNB is impossible, new signal and procedure forsynchronization establishment between UEs may be defined.

The UE which periodically transmits the D2D synchronization signal maybe referred to as a D2D synchronization source. When the D2Dsynchronization source is the eNB, the structure of the transmitted D2Dsynchronization signal may be the same as that of the PSS/SSS. When theD2D synchronization source is not the eNB (for example, the UE or theglobal navigation satellite system (GLASS)), a structure of thetransmitted D2D synchronization signal may be newly defined.

The D2D synchronization signal is periodically transmitted for a periodof not less than 40 ms. Each UE may have multiple physical-layersidelink synchronization identities. The D2D synchronization signalincludes a primary D2D synchronization signal (alternatively, a primarysidelink synchronization signal) and a secondary D2D synchronizationsignal (alternatively, a secondary sidelink synchronization signal).

Before transmitting the D2D synchronization signal, first, the UE maysearch the D2D synchronization source. In addition, when the D2Dsynchronization source is searched, the UE may obtain time-frequencysynchronization through the D2D synchronization signal received from thesearched D2D synchronization source. In addition, the corresponding UEmay transmit the D2D synchronization signal.

Hereinafter, for clarity, direct communication between two devices inthe D2D communication is exemplified, but the scope of the presentinvention is not limited thereto, and the same principle described inthe present invention may be applied even to the D2D communicationbetween two or more devices.

One of the D2D discovery methods is a method for performing, by alltypes of UE, discovery according to a dispersive method (hereinafterreferred to as “dispersive discovery”). The method for performing D2Ddiscovery dispersively is not a method for selecting and determining aresource (e.g., an eNB, UE, or D2D scheduling device) in one place likea centralized method, but is a method for determining and selecting, byall types of UE, discovery resources dispersively and sending andreceiving discovery messages.

In this patent, signals (or messages) periodically transmitted by typesof UE for D2D discovery may be hereinafter called discovery messages,discovery signals, or beacons. The signal (or message) is hereinaftercalled a discovery message, for convenience sake.

In dispersive discovery, a dedicated resource, that is, a resourcethrough which UE may send and receive a discovery message, may beperiodically allocated to the UE separately from a cellular resource.

FIG. 20 is a diagram showing an example of a discovery procedure betweentypes of UE.

As shown in FIG. 20, the dispersive discovery method may include threesteps, including (1) a beacon resource sensing procedure S2010, (2) aresource selection procedure S2020, and (3) a beacon transmission andreception procedure S2030.

First, in the beacon resource sensing procedure, all of types of UEperforming discovery may receive the resources of a discovery resourceregion during one period corresponding to the discovery resource regionaccording to the dispersive method.

In this case, the one period may be indicated by K and may be K=64 msec,that is, 64 subframes, for example.

Furthermore, the number of resources N received by all of the types ofUE may be 44 RBs (10 MHz).

The resource selection procedure refers to a procedure for dividingresources of a low energy level from sensed beacon resources andrandomly selecting beacon resources from a lower x % (x=a specificinteger, for example, 5, 7, 10, . . . ) of the divided resources.

In this case, the reason why the resources having a low energy level areselected is that there is a good possibility that types of surroundingUE may not use many discovery resources in the resources of a low energylevel. That is, this means that there are not many types of UEperforming discovery procedures which may cause interference nearby.

Accordingly, if UE uses a resource of a low energy level for a discoverypurpose, a probability that interference may occur when sending a beaconmay be low.

Furthermore, the reason why the resources are randomly selected withinthe predetermined lower x % is that a probability that the same resourcecorresponding to the lowest energy level may be simultaneously selectedby several types of UE is high if the resource of the lowest energylevel is selected is high. Accordingly, resources are randomly selectedwithin the predetermined % (a kind of pool of selectable resources isconfigured).

In this case, the value may be variably set depending on animplementation of a D2D system.

Furthermore, the discovery procedure needs to continue to be performedeven in an RRC_IDLE state in which connection with an eNB is not presentin addition to a radio resource control (RRC)_Connected state in whichconnection with an eNB is present.

The beacon transmission and reception procedure refers to a procedurefor randomly sending and receiving a discovery signal through a selectedresource.

A process for selecting a discovery resource in a discovery procedure indispersive D2D communication proposed in this specification is describedin more detail below with reference to FIGS. 21 to 28.

FIG. 21 is a flowchart illustrating an example of a method for selectinga discovery region in a discovery procedure proposed in thisspecification.

In the dispersive discovery method, a discovery resource that belongs toall of resources and that is used to send a discovery message (or adiscovery signal) is fixedly allocated. The fixedly allocated discoveryresource is periodically made available every time.

In this case, the discovery message includes data. If the discoverymessage does not include data, it may be represented as a discoverysignal.

First, in order to send a discovery message, UE has to select adiscovery resource to be used.

If the UE first performs a discovery procedure, it measures a receivedenergy level in the entire discovery resource region during one period(e.g., 64 subframes), that is, during a discovery period, at step S2110.

The UE selects a discovery resource to be used based on the measuredreceived energy level in order to send a discovery message at stepS2120.

In this case, the UE may select a resource having a measured receivedenergy level corresponding to a specific value or less or a specificvalue or higher.

That is, if the UE selects a resource having the smallest receivedenergy level, there is a high probability in which types of UE mayselect the same discovery resource placed at a similar (or close)position. Accordingly, the UE randomly selects a resource that belongsto resources having a received energy level corresponding to lower x %(x is a natural number) and that is used to send the discovery message.

Furthermore, if a resource through which a discovery message is to betransmitted is previously selected once using a predetermined hoppingpattern, a resource through which a discovery message is to betransmitted can be obtained according to a pattern equation or rule in anext discovery period.

Accordingly, the UE randomly selects a specific discovery resource fromresources having a received energy level corresponding to a specificvalue or less in a first discovery period at step S2120 and sends thediscovery message through the selected discovery resource at step S2130.

Furthermore, the UE sends a discovery message through a discoveryresource based on a predetermined hopping pattern from a next discoveryperiod at step S2140.

FIG. 22 is a diagram showing an example of a method for selecting adiscovery region in a discovery procedure proposed in thisspecification.

FIG. 22 shows an example in which types of UE, for example, UE A and UEB placed at a long distance randomly select specific regions ofresources having received signal energy corresponding to lower x %.

FIG. 22 shows the results of received energy of all of resources (ordiscovery resource regions, discovery resource intervals, or discoveryradio resource pools) measured by the UE A and the UE B placed at a longdistance in order to select discovery resources at the same time.

In this case, one rectangle 2210 is indicative of one resource unit, ablue area 2220 is indicative of a received energy value, and a red line2230 is indicative of the threshold value “x” of received energy.

That is, in FIG. 22, a resource having a received energy value lowerthan the red line is a resource 2240 belonging to the lower x %.

From FIG. 22, it may be seen that similarity between the received energylevels measured by the UE A and the UE B is not high if the UE A and theUE B are sufficiently spaced apart from each other.

FIG. 22 shows an example in which a total of 16 resources are presentand a resource for selecting a discovery resource is selected at a lower25%.

Each of the UE A and the UE B randomly selects one of four resourceshaving a low received energy level and performs transmission from a nextdiscovery period.

The number of resources that overlap when the UE A and the UE B selectdiscovery resources from the lower four resources is only one resource.Accordingly, a probability in which the UE A and the UE B may select thesame resource is 1/16.

FIG. 23 is a diagram showing another example of a method for selecting adiscovery region in a discovery procedure proposed in thisspecification.

FIG. 23 shows an example in which types of UE, for example, UE A and UEB placed at a short distance randomly select specific regions ofresources having a received signal energy level corresponding to lower x%.

FIG. 23 shows the results of received energy of all of resources (ordiscovery resource regions) measured by the UE A and the UE B placed ata short distance in order to select discovery resources at the sametime.

From FIG. 23, it may be seen that similarity between the received energylevels measured by the UE A and the UE B is very high because the UE Aand the UE B are placed at a very short distance.

Likewise, one rectangle 2310 is indicative of one resource unit, a bluearea 2320 is indicative of a received energy value, and a red line 2330is indicative of the threshold value “x” of received energy.

That is, in FIG. 23, a resource having a received energy value lowerthan the red line is a resource 2340 belonging to the lower x %.

FIG. 23 shows an example in which a total of 16 resources are presentand a resource for selecting a discovery resource is selected at a lower25%.

Accordingly, a probability in which the UE A and the UE B may select thesame resource when selecting discovery resources from the lower fourresources is high compared to the example of FIG. 22. FIG. 23corresponds to a case where all of four selected resources have beendesignated as the same lower resources. A probability in which the UE Aand the UE B may finally select the same discovery resource in order toselect discovery messages is ¼.

A resource collision problem occurring because types of UE, for example,UE A and UE B select the same hopping pattern and a method for solvingthe resource collision problem are described in more detail below.

FIG. 24 illustrates that a collision between resources is generatedbecause the same hopping pattern that has been previously defined (orpredefined) is selected after a discovery resource is selected (in ani-th discovery period).

FIG. 24 shows a problem occurring when types of UE, for example, UE Aand UE B continue to select the same discovery resource.

That is, as shown in FIG. 24, if the UE A and the UE B select the samediscovery resource in an i-th D2D discovery period, discovery resourcesto be used in subsequent discovery periods are determined according to ahopping pattern. Accordingly, the UE A and the UE B continue to selectthe same discovery resource and use the same discovery resource. In thiscase, in general, two problems may be generated.

First, the UE A and the UE B cannot discover them each other. Second,other types of UE placed near the UE A and the UE B cannot discover theUE A and the UE B.

Although a probability in which a collision between resources may occuris not high in FIG. 24, if a collision between resources is generated inFIG. 24, it causes inconvenience in the operation of a discoveryprocedure.

Furthermore, if an environment in which the start of the operation of adiscovery procedure becomes more frequent (e.g., an environment in whichwhen D2D communication is actually started, types of UE stop theirdiscovery operations and newly start discovery again after the D2Dcommunication is terminated or an environment in which types of UE mayfrequently turn on and off their D2D communication functions) is takeninto consideration, a collision between resources in FIG. 24 may cause abig problem.

A method for solving the discovery resource collision in FIG. 24 isdescribed in more detail below with reference to FIGS. 25 to 28.

FIG. 25 is a flowchart illustrating an example of a method forpreventing a resource collision problem which may occur in a discoveryprocedure proposed in this specification.

In FIG. 25, there is proposed a resource clustering (or grouping)-basedhopping method in order to prevent a resource collision problem whichmay occur in a discovery procedure.

Resource clustering based on the hopping method refers to a method forgrouping multiple discovery resource units (or multiple units) withoutdetermining a hopping pattern for each discovery resource unit anddefining a hopping pattern for each group.

More specifically, each of types of UE first selects a discoveryresource of a specific group for discovery at step S2510. Each of typesof UE which belong to the specific group or have selected the specificgroup selects a random discovery resource (i.e., selects a discoveryresource unit) every period, for each designated time/point of time, orfor each designated subframe index or subframe number within thespecific group at step S2520.

Thereafter, each of the types of UE sends a discovery message throughthe selected discovery resource at step S2530. Accordingly, a resourcecollision problem which may occur in a discovery procedure can besolved.

In this case, the size of the group and the size of the discoveryresource unit when the discovery resource is randomly selected may bevariously set.

Furthermore, the group may be determined using channel information, suchas a radio resource management (RRM) report (e.g., RSRP or RSRQ) orinformation about the positioning of UE.

For example, types of UE having the same signal to interference ratio,the same signal to interference/noise ratio, or the same signal qualityvalue may be determined to be the same group.

In particular, types of UE may be grouped based on proximity throughposition-based information, such as a GPS.

A resource may be allocated to a UE group determined accordingly, and UEmay select a discovery resource through random selection within thegroup.

In this case, a higher layer may allocate a group resource to specificUE through an RRC signal. The specific UE may randomly select a resource(or a resource unit or resource group) within the group resource and usethe resource for discovery.

That is, the higher layer allocates a group resource region to the UEthrough a UE-specific RRC signal so that the UE randomly selects oneresource block of the allocated group resource region.

One or more resource blocks are allocated to UE semi-statically, and theuse of a specific region block of the one or more resource blocksdepends on the randomness of the UE.

FIG. 26 is a diagram showing an example of a method for preventing aresource collision problem in a discovery procedure proposed in thisspecification.

FIG. 26 shows that two resource units form one group. That is, in FIG.26, the size of a resource group is 2.

That is, although types of UE, for example, UE A and UE B select thesame discovery resource group, they can select different resourcesthrough random selection while hopping within the selected discoveryresource group. Accordingly, a resource collision phenomenonattributable to the selection of the same discovery resource can beprevented.

In FIG. 26, a bundle of two resources 2610 (i.e., a group size=2resource units) indicated by a deviant crease line in blue correspondsto one group.

The position of the blue group 2610 is changed according to a hoppingpattern every discovery period. In this case, the UE A and the UE B donot select one discovery resource unit in order to send discoverymessages, but select one discovery resource group.

As a result, although the UE A and the UE B select the same group, theywill randomly select resources to be used every discovery period withinthe selected group.

Accordingly, although the UE A and the UE B have selected the sameresource in an i-th region and an (i+1)-th period, they can selectdifferent resources in an (i+2)-th period, thereby being capable ofavoiding a resource collision between the UE A and the UE B.

In other words, the resource group is deterministically maintained. Ifrandomness in the selection of resources within a group is added,however, a situation in which discovery is impossible can be solved whenthe UE A and the UE B select the same resource at the same time.

FIG. 27 is a diagram showing another example of a method for preventinga collision between resources in a discovery procedure proposed in thisspecification.

FIG. 27 shows that four resource units form one group 2710.

That is, in FIG. 27, the size of the resource group is 4.

As shown in FIG. 27, although types of UE, for example, UE A and UE Bhave selected the same pattern, a probability in which the UE A and theUE B may use the same discovery resource every discovery period is lowcompared to a case where the size of a resource group is 2.

In this case, if the size of the resource group is great, it means thatthe number of users selecting the same group is many.

Accordingly, if the number of resources is sufficiently larger than thenumber of users, the same advantage may be obtained by increasing thesize of a resource group. If the number of resources is smaller than thenumber of users, however, the size of a resource group may be reduced inorder to prevent many users from selecting the same group.

Accordingly, the size of a resource group may be variably determineddepending on the number of resources and the number of users.

FIG. 28 is a diagram showing yet another example of a method forpreventing a collision between resources in a discovery procedureproposed in this specification.

FIG. 28 shows that a resource group is extended to a concept of aplurality of groups and shows that one resource group is divided into aplurality of smaller groups.

That is, each of types of UE may select each of a plurality of groups,may perform random selection between a plurality of smaller groupswithin the selected group, and may select a resource for D2D discoveryby performing random selection in a resource unit level within therandomly selected group.

Referring to FIG. 28, UE may first select a resource group 1 2810 (agroup size=8), may select a group 2 by performing random selection on agroup 2 2820 (a group size=4) within the group 1, may select a group 3by performing random selection on group 3 2830 (a group size=2) withinthe selected group 2, and may select a discovery resource through whicha discovery message is to be transmitted through random selection in aresource unit level in the selected group 3.

That is, if resources are grouped using a hierarchical structure fordiscovery and random selection is applied in a group level and resourceunit level as in FIG. 28, a proper advantage for sending a discoverymessage can be guaranteed because a collision between resources isprevented.

In an embodiment, assuming that a total number of resources is N and agroup size is M (M≤N), the method of FIG. 28 may be advantageously usedwhen the number of types of UE discoverable near UE is smaller than N/M.

The reason for this is that a total number of types of UE can be checkedfrom the standpoint of a network. Accordingly, a proper M value may beset using the number of resources and the number of types of UE per areabased on a probabilistic approach.

In this case, in an environment in which the number of types of UE isvery large, not to perform resource clustering may be more advantageous.Accordingly, if a system is operated by adding a parameter capable ofenabling or disabling resource clustering and M as a parameter,discovery can be performed more efficiently.

As described with reference to FIGS. 25 to 28, if a plurality oftransmission unit resources (or transmission resource units) is groupedand expanded to one group transmission unit, energy (or interference)components of different levels may be detected in each of thetransmission unit resources within a group.

For example, if the size of a group transmission unit is M, one groupmay be defined by grouping M transmission unit resources.

It is assumed that UE has detected an energy level by scanning the onegroup resource and as the results of the detection, a small amount ofenergy has been detected in a No. 1 transmission unit resource and alarge amount of energy has been detected in a No. 2 transmission unitresource.

In this situation, the UE has to determine that it is advantage to senda signal or packet through a resource having a low energy level.

If some resources within a group resource have a low energy level andsome resources within the group resource have a high energy level,whether or not to send a signal or packet through the group resource maybe determined based on the ratio of the high and low energy levels.

Assuming that M=4, if energy is not detected in 3 of four transmissionunit resources or an energy level is low in the 3 transmission unitresources, D2D UE may select one of the 3 transmission unit resourcesand rules on which transmission is started.

In this case, the ratio of high and low energy levels is a 50:50 rule.If an interference or energy level is low in only 2 transmission unitresources, one of the 2 transmission unit resources may be selected andtransmission may be started.

Furthermore, it may be difficult for UE to certainly check whether aninterference or energy level is low or high in a corresponding resourceunit region through one scanning.

In this case, the scanning procedure of D2D UE may be advantageouslyperformed over a plurality of subframes or periods.

In this case, a plurality of subframes may be defined as a scanningwindow. The scanning window may be set as a different value by takinginto consideration a situation in each system.

In another rule, the same rule is used for all of transmission unitresources within a group.

As a result, the results of the sensing of resources may be shared bytypes of D2D UE for each group. That is, metric to which reference willbe made upon transmission may be produced by averaging energy levelsdetected in a group unit or taking into consideration other parameters(e.g., in-band emission), and whether or not to send a signal or packetthrough a corresponding group resource may be determined based on themetric.

For example, operations according to the metric may be previouslydefined, such as that transmission is impossible when the metric is ‘0’,potential transmission is possible when the metric is ‘1’, andtransmission must be performed when the metric is ‘2’.

In an embodiment, the metric may be calculated based on a previouslydesignated parameter. Whether actual transmission will be performed maybe determined by UE individually and autonomously so that a resource maybe allocated.

If a random allocation method is used to allocate resources within agroup, a method for selecting an energy level having the greatest valueby performing sensing/energy detection on the resources within the groupand performing transmission may be advantageous.

A resource unit that belongs to transmission resource units within agroup and has a high energy level may mean that transmission has beenperformed. Accordingly, there is a good possibility that transmissionmay not be performed in the corresponding resource unit in a nexttransmission opportunity.

Accordingly, if such a probabilistic approach method is taken intoconsideration, a collision between the resources of types of UE can beminimized by selecting a resource unit having a high energy level andperforming transmission in a next transmission opportunity through theselected resource unit.

The transmission of a discovery message has been chiefly described withreference to the methods of FIGS. 21 to 28, but the methods of FIGS. 21to 28 may be likewise applied to determine the transmission resource ofa D2D communication channel for D2D communication or to determine thetransmission resource of a synchronization channel and signal.

Internal Block Diagrams of UE and eNB

FIG. 29 is a diagram showing an example of the internal block diagramsof UE and an eNB may be implemented in the methods proposed in thisspecification.

As shown in FIG. 29, the eNB 2910 and the UE 2920 include communicationunits (or transmission/reception units or radio-frequency (RF) units)2913 and 2923, processors 2911 and 2921, and memory 2912 and 2922,respectively.

Each of the eNB and the UE may further include an input unit and anoutput unit.

The communication unit 2913, 2923, the processor 2911, 2921, the inputunit, the output unit, and the memory 2912, 2922 are functionallycoupled in order to perform the methods proposed in this specification.

When receiving information produced by a physical layer (PHY) protocol,the communication unit (or the transmission/reception unit or the RFunit) 2913, 2923 moves the received information to an RF spectrum,performs filtering and amplification on the information, and sends thesignal to an antenna. Furthermore, the communication unit moves the RFsignal, received from the antenna, to a band that may be processed inthe PHY protocol and performs filtering on the RF signal.

Furthermore, the communication unit may have a switch function forchanging such transmission and reception functions.

The processor 2911, 2921 implements the functions, processes and/ormethods proposed in this specification. The layers of a radio interfaceprotocol may be implemented by the processor.

The processor may be represented as a control unit, controller, controlunit, or computer.

The memory 2912, 2922 is connected to the processor 2911, 2921 andstores protocols or parameters for performing D2D discovery.

The processor 2911, 2921 may include application-specific integratedcircuits (ASICs), other chipsets, logic circuits and/or data processingdevices. The memory may include read-only memory (ROM), random accessmemory (RAM), flash memory, a memory card, a storage medium and/or otherstorage devices. The communication unit may include baseband circuitsfor processing radio signals. When an embodiment is implemented insoftware, the method may be implemented as a module process or functionfor performing the functions.

The module may be stored in the memory and may be executed by theprocessor. The memory may be placed inside or outside the processor andmay be connected to the processor by well-known means.

The output unit (or display unit) is controlled by the processor andoutputs information output by the processor along with a key entrysignal generated from a key input unit and various information signalsfrom the processor.

Furthermore, the drawings have been divided and described forconvenience of description, but the embodiments described with referenceto the drawings may be merged to implement a new embodiment(s).Furthermore, the scope of the present invention also includes designinga computer-readable recording medium in which a program for executingthe aforementioned embodiments has been written according to the needsof those skilled in the art.

D2D discovery according to this specification is not limited and appliedto the configurations and methods of the aforementioned embodiments, butsome or all of the embodiments may be selectively combined andconfigured so that the embodiments are modified in various ways.

In this specification, D2D discovery may be implemented in a recordingmedium, readable by a processor included in a network device, in theform of code readable by the processor. The processor-readable recordingmedium includes all types of recording devices in which data readable bya processor is stored. The processor-readable recording medium mayinclude ROM, RAM, CD-ROM, magnetic tapes, floppy disks, and optical datastorages, for example. Furthermore, the processor-readable recordingmedium may be implemented in the form of carrier waves, such astransmission over the Internet.

Furthermore, the processor-readable recording medium may be distributedto computer systems connected over a network, and code readable by aprocessor may be stored in the processor-readable recording medium andexecuted in a distributed manner.

INDUSTRIAL APPLICABILITY

In this specification, a D2D communication method is used in a wirelesscommunication system.

The invention claimed is:
 1. A method for transmitting, by a first userequipment (UE), a discovery message based on device to device (D2D)communication in a wireless communication system, the method comprising:receiving, from a base station, information related to a discoveryresource region including a plurality of discovery resource groups;selecting, a specific discovery resource group from the discoveryresource region; selecting, randomly, a sub-discovery resource groupfrom the selected specific discovery resource group, wherein thesub-discovery resource group includes a plurality of discovery resourceunits, wherein the discovery resource group includes a plurality ofsub-discovery resource groups; selecting, randomly, a discovery resourceunit for transmitting a discovery message from the selectedsub-discovery resource group; and transmitting, to a second UE, thediscovery message on the selected discovery resource unit, wherein theplurality of sub-discovery resource groups are configured based on asize of the discovery resource group, a number of discovery resourceunits in the discovery resource region, and a number of different UEsdiscoverable around the first UE.
 2. The method of claim 1, furthercomprising: monitoring the discovery resource region, wherein thediscovery resource region comprises 64 subframes.
 3. The method of claim1, wherein the discovery resource unit is randomly selected perdiscovery period.
 4. The method of claim 1, wherein the discoverymessage is transmitted based on a ratio of high and low energy levels ofthe at least one discovery resource unit within the selectedsub-discovery resource group.
 5. The method of claim 1, wherein theplurality of sub-discovery resource groups are configured when thenumber of different UEs discoverable around the first UE is smaller thana value obtained by dividing a number of discovery resource units in thediscovery resource region by the size of the discovery resource group.6. A first user equipment (UE) for transmitting a discovery messagebased on device to device (D2D) communication in a wirelesscommunication system, the first UE comprising: a transmitter and areceiver; and a processor operatively coupled to the transmitter andreceiver, wherein the processor is configured to: control the receiverto receive, from a base station, information related to a discoveryresource region including a plurality of discovery resource groups;select, a specific discovery resource group from the discovery resourceregion; select, randomly, a sub-discovery resource group from theselected specific discovery resource group, wherein the sub-discoveryresource group includes a plurality of discovery resource units, whereinthe discovery resource group includes a plurality of sub-discoveryresource groups; select, randomly, a discovery resource unit fortransmitting a discovery message from the selected sub-discoveryresource group; and control the transmitter to transmit, to a second UE,the discovery message on the selected discovery resource unit, whereinthe plurality of sub-discovery resource groups are configured based on asize of the discovery resource group, a number of discovery resourceunits in the discovery resource region, and a number of different UEsdiscoverable around the first UE.
 7. The first UE of claim 6, whereinthe processor is further configured to: monitor the discovery resourceregion, wherein the discovery resource region comprises 64 subframes. 8.The first UE of claim 6, wherein the discovery resource unit is randomlyselected per discovery period.
 9. The first UE of claim 6, wherein thediscovery message is transmitted based on a ratio of high and low energylevels of the at least one discovery resource unit within the selectedsub-discovery resource group.
 10. The first UE of claim 6, wherein theplurality of sub-discovery resource groups are configured when thenumber of different UEs discoverable around the first UE is smaller thana value obtained by dividing a number of discovery resource units in thediscovery resource region by the size of the discovery resource group.